A microcantliever based crack healing experiment is described and utilized in order to study the capillary nucleation rate for typical MEMS surfaces. An advanced test chamber that allows exquisite environmental control is also described and used in this study. Crack healing experiments prove to be a viable experimental technique to investigate the dynamics of capillary nucleation. The effective capillary nucleation time for the multi-asperity surface of microcantilever samples appears to increase logarithmically with adhesion energy.

We present an integrated readout technique for interrogating the suspension height of micro-electro-mechanical systems (MEMS) structures. This readout technique is envisaged to be useful in applications such as MEMS-based biological and chemical sensing, where it is necessary to obtain the accurate position of a MEMS beam. The approach is based on the suspended MEMS structure modulating light transmission in an underlying optical waveguide via Fabry-Perrot phenomena. The performance of the technique is predicted via finite difference time domain (FDTD) simulations the results of which are confirmed by experimental measurements.

Electrokinetic based micro- and nanofluidic technologies provide revolutionary opportunities to separate, identify and analyze biomolecular species. Key to fully harnessing the power of such systems is the development of a robust method for integrated electrodes as well as a thorough understanding of the influence of the electrokinetic surface properties with and without different surface modifications. In this work, we demonstrate a surface micromachined fabrication approach for integrated addressable metal electrodes within centimeter-long nanofluidic channels using a low-temperature, xenon diflouride dry-release method for novel biosensing applications, as well as recent results from a joint theoretical and experimental study of electrokinetic surface properties in nano- and microfluidic channels fabricated with fused silica. The main contribution of this fabrication process involves the addition of addressable electrodes to a novel dry-release channel fabrication method, produced at <300°C, to be used in nanofluidic electronic sensing of biomolecules. Finally, we also show a novel method with which to coat our channels with silane based chemistries. Certain modifications are observed to show improved resistance to non-specific adhesion of both small molecules and proteins, indicating their further use as compatible surfaces in micro- and nanofluidic applications.

Flexible electronics and microsystems are an emerging technology with a tremedous impact to the future electronics and information technology and widespread applications. Various devices and microsystems have been developed. Surface acoustic wave (SAW) devices are a type of essential device for electronics, microsensors and microsystems; however there is no activity on the development of flexible SAW devices yet. This paper reports the development of flexible SAW devices on cheap, bendable and disposable plastic films. Flexible SAW devices with resonant frequency of 198.1 MHz and 447 MHz for the Rayleigh and Lamb waves respectively have been obtained with a large transmission signal up to 18dB. The flexible SAW devices have also demonstrated their ability for acoustic streaming with a velocity up to 3.4 cm/s and for particle concentration. The results have clearly demonstrated that the flexible SAW devices have great potential for applications in electronics and microsystems.

A MEMS floating element shear stress sensor has been developed for flow testing applications, targeted primarily in ground and flight testing of aerospace vehicle and components. However, concerns remain about the interaction of the flow with the mechanical elements of the structure at the micro-scale. In particular, there are concerns about the validity of laminar flow cell calibration to measurement in turbulent flows, and the extent to which pressure gradients may introduce errors into the shear stress measurement. In order to address these concerns, a numerical model of the sensor has been constructed.

In this paper, a computational fluid dynamics (CFD) model is described. The CFD model directly models a laminar flow cell experiment that is used to calibrate the shear sensor. The computational model allows us to quantify the contributions (e.g. pressure gradient vs. shear, top surface vs. lateral surfaces) to the sensor output in a manner that is difficult by purely experimental means. The results are compared to experimental data, validating the model and resulting in the following: Surface shear stress contributes approximately 40% of the total flow direction force; pressure gradient effects contribute nearly 45% for the textured shuttle described here; lift forces and pitching moments are non-zero. Thus, it is found that flow interactions are complex and that it is insufficient to simply assume that flow forces on the sensor are the top area multiplied by wall shear, as is sometimes done. Pressure gradient effects, at least, must be included for accurate calibration.

The measurement of precise submicron displacements is essential in several MEMS applications. For instance, the measurement of the mechanical parameters of biological cells requires repeatable measurement of displacements in the nanometer regime. This paper presents a method to make displacement measurements in an aqueous MEMS environment with a ± 10 nm accuracy by using the blue channel of RGB pictures in combination with a FFT phase shift analysis.

KNbO3 films were prepared at 100 - 240°C on (100)cSrRuO3//(100)SrTiO3 substrates by hydrothermal method using KOH and Nb2O5 as source materials. The incubation time before starting deposition and the deposition rate after starting deposition increased and decreased with decreasing deposition temperature, respectively. Epitaxial {100}c-oriented KNbO3 films with 300 nm thick were successfully obtained at 100°C on (100)cSrRuO3//(100)SrTiO3 substrates for 144 h. We observed the typical butterfly-shape strain curves originated from the piezoelectricity for the first time for KNbO3 films deposited down to 120°C.

Fixed-fixed beams are ubiquitous MEMS structures that are integral components for sensors and actuation mechanisms. However, residual stress inherent in surface micromachining can affect the mechanical behavior of fixed-fixed structures, and even can cause buckling. A self-tensioning support post design that utilizes the compressive residual stress of trapped sacrificial oxide to control the stress state passively and locally in a fixed-fixed beam is proposed and detailed. The thickness and length of the trapped oxide affects the amount of stress in the beam. With this design, compression can be reduced or even converted into tension. An analytical model and a 3D finite element model are presented. The analytical model shows relatively good agreement with a 3D finite element model, indicating that it can be used for design purposes. A series of fixed-fixed beams were fabricated to demonstrate that the tensioning support post causes a reduction in buckling amplitude, even pulling the beam into tension. Phase shifting interferometry deflection measurements were used to confirm the trends observed from the models. Controlling residual stress allows longer fixed-fixed beams to be fabricated without buckling, which can improve the performance range of sensors. This technique can also enable local stress control, which is important for sensors.

There has been a recent resurgence in interest in developing ohmic switches to complement transistors in order to address challenges associated with electrical current leakage. A critical limitation in ohmic switches remains the reliability of their electrical contacts. These contacts are prone to hydrocarbon induced contamination which progressively inhibits signal transmission, eventually leading to device failure. We report on progress made towards controlling the contamination phenomenon. We discuss how contact materials and operating environment affect device performance, showing that RuO2 coated microswitch contacts operating in the presence of O2 experience very limited contaminant accumulation even in hydrocarbon-rich environments. We then demonstrate that devices which have experienced contamination can recover their original performance by being operated in clean N2:O2 environment. Finally, we suggest that this resistance recovery is associated with the chemical transformation of the contaminant as opposed to its removal and that the transformed contaminant may shield the Pt coating from oxidation.

Optical control is a reversible and convenient technology, able to be measured in real-time, which makes it excellent for application to microfluidic, biomechanical, and electro-mechanical devices. These advantages are especially attractive for photo-responsive materials. In this study, we developed a new photo-responsive, electrostrictive material from a composite material made by mixing a dielectric polymer P(VDF-TrFE-CFE) and an organic photoconductive material TiOPc. The photo-responsibility of the material has been validated by corresponding actuators. We found that under white light illumination, deformation will increase which can be attributed to a decrease in the TiOPc impedance. We identified that the optimal TiOPc concentration for actuator applications is 10% P(VDF-TrFE-CFE)/TiOPc. Moreover, controlling the fluid flow within the capillary tube through light illumination also validated the photo-responsive actuator. Our results show that the mechanism and the photo-responsive material can be used to pursue further study on light controlling microfluidic, and related electro-mechanical devices.

Flexible surface acoustic wave (SAW) based temperature and humidity sensors were fabricated and characterized. ZnO piezoelectric films were deposited on polyimide substrates by DC magnetron sputtering. ZnO films possess (0002) crystal orientation with large grain sizes of 50∼70 nm. SAW devices showed two wave modes, namely the Rayleigh and Lamb modes, with the frequencies at f R ∼132MHz and f L ∼427MHz respectively for a wavelength of 12 μm device. The two resonant frequencies have a temperature coefficient of frequency (TCF) of −423ppm/K and −258ppm/K for the Rayleigh and Lamb waves, respectively. The SAW sensors exhibited a good repeatability in responding to cyclic change of humidity. The responses of the sensors increase with the increase in humidity, and the sensitivity increases with the decrease in wavelength. A high sensitivity of 34.7 kHz/10%RH has been obtained from a SAW device without any surface treatment, demonstrated that the flexible SAW humidity sensors are very promising for application in flexible sensors and microsystems.

Surface plasmon polaritons (SPPs), which are coupled excitations of electrons bound to a metal-dielectric interface, show great potential for application in future nanoscale photonic systems due to the strong field confinement at the nanoscale, intensive local field enhancement, and interplay between strongly localized and propagating SPPs. The fabrication of sufficiently smooth metal surface with nanoscale feature size is crucial for SPPs to have practical applications. A template stripping (ST) method combined with PMMA as a template was successfully developed to create extraordinarily smooth metal nanostructures with a desirable feature size and morphology for plasmonics and metamaterials. The advantages of this method, including the high resolution, precipitous top-to bottom profile with a high aspect ratio, and three-dimensional characteristics, make it very suitable for the fabrication of plasmonic structures. By using this ST method, boxing ring-shaped nanocavities have been fabricated and the confined modes of surface plasmon polaritons in these nanocavities have been investigated and imaged by using cathodoluminescence (CL) spectroscopy, which has been turned out to be a powerful means to characterize the resonant SPPs modes confined in metal nanocavities [1∼5] . The mode of the out-of-plane field components of surface plasmon polaritons dominates the experimental mode patterns, indicating that the electron beam locally excites the out-of-plane field component of surface plasmon polaritons. Quality factors can be directly acquired from the spectra induced by the ultrasmooth surface of the cavity and the high reflectivity of the silver (Ag) reflectors. Because of its three-dimensional confined characteristics and the omnidirectional reflectors, the nanocavity exhibits a small modal volume, small total volume, rich resonant modes, and flexibility in mode control. Numerous applications, such as plasmonic filter, nanolaser, and efficient light-emitting devices, can be expected to arise from these developments.

We report the Eu doping induced improvement on the second harmonic generation (SHG) of ZnO nanowires and correlates with the structural modification and corresponding linear absorption. A non-monotonic enhancement in the SHG emission is observed with the increase of Eu concentration. To understand the underlying mechanism, the effective second order non–linear coefficient (deff) is calculated from the theoretical fitting with considering the absorption effect. The highest deff (19.09±0.11 pm/V) is obtained for the 1 at.% Eu doped ZnO nanowires, which is several times larger than the standard SHG material β-BaB2O4 (BBO). Dependence of the deff with the Eu doping, structural modification and absorption magnitude are systematically discussed.

ZnO nanowire (NW) arrays were examined with Transmission Electron Microscopy (TEM) in cross-section after preparation by Focused Ion Beam (FIB) milling. This technique revealed that ZnO nanowires grown using a Au catalyzed vapor technique typically have Au particles at the NW tips, and also randomly dispersed across the base crystal growth that joins adjacent NWs. It is shown the adjacent NWs and the combined base growth is one crystal structure which can be used as a back electrical contact making fabrication of vertical array devices possible. However, the base growth displays detrimental features such as embedded Au particles and lattice defects which can affect the electrical output through depletion regions and scattering centers. In an effort to overcome these problems we investigate a growth method that is nucleated through a minor alteration of the a-plane sapphire surface roughness via a weak chemical etch. Observations of various stages of the growth show the growth nucleates as separate nanoislands that grow in c-plane alignment with Sapphire (1-210), and as growth continues these islands meet and form a polycrystalline film. Further growth initiates nanowire growth and the formation of a single crystal base layer and NW structure that can cover several square millimeter’s. This allows high quality arrays that are relatively free from defects to be formed without any metals contamination and ready for further device processing.

Single-walled carbon nanotube (SWCNT) growth were carried out on SiO2/Si substrates using Pt catalysts at different temperatures, from 400°C to 700°C, under various ethanol pressures by an alcohol gas source method, a type of cold-wall chemical vapor deposition (CVD). Raman measurements showed that the optimal ethanol pressure decreased as the growth temperature was reduced, and that SWCNTs grew even at 400°C by optimizing the ethanol pressure to 1×10-5 Pa in a high vacuum system. Compared to the SWCNTs grown from Co catalysts, the diameters of SWCNTs grown from Pt were smaller, irrespective of the growth temperature. In addition, both the SWCNT diameter and the distribution became narrower by reducing the growth temperature and we obtained small-diameter SWCNTs of which the diameters were less than 1 nm using Pt catalysts.

We report the fabrication and characterization of supercapacitors prepared on a flexible substrate using a printable, high-viscosity carbon nanotube (CNT) ink. The CNT-hemicellulose composite ink was prepared using ultrasonication and applied on the substrate with a doctor blade. Aqueous sodium chloride was used as electrolyte. The capacitance of the supercapacitors was 16 mF for a device size of 2 cm2. The measurements were carried out in accordance to an international standard for electric double layer capacitors.

Carbon nanotube field effect transistors (CNT FETs) have many possible applications in future nano-electronics due to their excellent electrical properties. However, one of the major challenges regarding their performance is the noticeable gate hysteresis which is often displayed in their transfer characteristics. The hysteresis phenomenon is often attributed to water-mediated charge transfer between the CNT and the dielectric layer or the CNT and the water layer itself. In this study, we implement three different experimental techniques and provide evidence that the hysteresis phenomenon of suspended CNT FETs, as well as of on-surface CNT FETs which operate at low gate voltage regimes (| Vg | < 3V), is based on gate-induced, water-assisted redistribution of mobile charge on the SiO2 surface, and it is not related to charge injection from the CNT itself. Two techniques are based on the current measurements through the CNT and the third utilizes electrostatic force microscopy (EFM) setup. In addition, the applied external gate voltage affect the relaxation time of the current. This change arises from the modification of the amount of water layers which adsorb onto the dielectric surface, which caused by dielectrophoresis attraction between the water molecules and the substrate. It is found that the relaxation time, and hence the surface conductivity, are very sensitive for the first few layers, and saturates above three monolayers of water molecules.

We analyze and compare optoelectronic properties and hot carrier relaxation dynamics in different forms of TiO2 anatase materials: nanowires and thin films. The models are chosen in such way that the same crystallographic surfaces are exposed and any difference in properties is attributed to the change of the dimensionality of the nanostructure. Specifically, we give a brief review of the electronic properties and non-adiabatic excited state dynamics of <001> anatase TiO2 nanowire as well as (100) and (001) anatase TiO2 surfaces. The calculated band gap of nanowire is larger than the ones of surfaces. The hole relaxation rate is higher than the electron relaxation rate for both the surfaces and nanowire, and the electron and hole relaxation rates of surfaces are larger than the ones of nanowire.

Recently, Fickenscher et al. [1] have shown that, in a core-multi-shell structure where a GaAs quantum well is embedded into an AlGaAs shell wrapped around a [111] oriented GaAs nanowire, the electron and hole ground states are strongly confined to the corners of the hexagonally symmetric quantum well. Thus this confinement defines quantum wires which run along the length of the nanowires along its corners. Here we review single nanowire photoluminescence measurements which show the significant confinement energy of the excitons. For well widths larger than 5 nm, optical transitions between electron and hole excited states can be seen in excitation spectra, while for widths less than 5 nm only the ground state optical transitions are observed. For well widths smaller than 5 nm, high resolution spatially resolved photoluminescence measurements show directly the appearance of localized states. Single nanowire spectra from the 4 nm QWT sample display ultranarrow emission lines on the high energy side of the luminescence band. Spatially-resolved PL images show that these quantum dots are localized randomly along the length of the wire.

We use Raman scattering to study the spatially-resolved strain and stress in a complex zinc blende GaAs/GaP heterostructured nanowire which contains both axial and radial interfaces. The nanowires are grown by metal-organic chemical vapor deposition in the [111] direction with Au nano particles as catalysts, High spatial resolution Raman scans along the nanowires show the GaAs/GaP interface is clearly identifiable. We interpret the phonon energy shifts in each material as one approaches the interface.