Thin-film MEMS molecular sensors are fabricated at temperatures below 110°C on glass substrates. The microelectromechanical structure consists of a surface micromachined bilayer bridge of phosphorous-doped hydrogenated amorphous silicon and aluminum with a patterned SiO2 layer on the top. Specific binding of DNA to functionalized SiO2 on the bridge is confirmed using fluorescence microscopy. Microbridges are electrostatically actuated and the resonance frequency measurements are performed in vacuum in the initial state after fabrication, after the chemical functionalization of the SiO2surface and after DNA immobilization. The sensor is able to detect the functionalization molecular layer, the cross-linker molecular layer, and the DNA molecules attached to the surface through a shift in its resonance frequency. The binding of molecules to the surface results in a shift of the resonance frequency due to contributions from surface stresses and mass loading.

Piezoelectric materials convert mechanical to electrical energy under stretching and bending conditions. Optimizing the coupling conversion is imperative to the electromechanical behavior of a micromachined membrane's performance. This paper discusses analytical calculations that were devised to determine the microscale structure that minimizes residual stress and outlines the implementation of fabrication technique variations including three different electrode configurations, trenching around the membrane, and reducing the total composite residual stress of the support structure using compressive silicon oxide. Lead zirconacte titanate (PZT) films between 1 and 3 μm thick with a ratio of Zr to Ti of 40:60 were deposited onto 3 mm square silicon membranes. The total tensile stress in the composite structure reaches 100 MPa during standard fabrication processing. Utilizing analytical calculations, a structure was determined that lowered the residual stress of the composite to 11 MPa and increased the electromechanical coupling 35 times. Changing the geometry of the electrode coverage decreased the residual stress of the composite by 40%. Trenching around the membrane provided a membrane with boundary conditions that approached simply supported and decreased the composite residual stress by another 16%. A comparison of the electromechanical behavior for these structures will be discussed, showing a route towards increasing electromechanical coupling in PZT MEMS.

Conducting polymer nanostructures such as nanofibers and nanotubes have potential uses in a variety of applications including electronic and photonic devices and sensors. Conducting polymers have also been used as artificial muscles. In this work, template synthesis method for fabricating solid polypyrrole nanowires and polypyrrole-gold nanowire heterostructures is demonstrated to explore suitability of these structures as nano-artificial muscles or nanoactuators. Polypyrrole nanowires are evaluated in an aqueous electrolyte to see if they retain the ability to expand and contract under electrochemical cycling. Template synthesis is then used to alternatively electroplate gold and electropolymerize polypyrrole in the pores of an alumina membrane to create layered polypyrrole-gold nanowires.

Properly designed sequences of oligonucleotides can be employed as scaffolds or templates for the self-organization of nanostructures and devices, through the Watson-Crick base pairing mechanism which serves as a programmable smart glue. In this paper, we report the Platinum metallization of peptide nucleic acid (PNA) sequences for the first time. PNA is an analogue of DNA and has a neutral backbone which provides stronger hybridization, greater stability and higher specificity in base pairing. Pt ions were reduced from a salt solution and localized over the PNA fragments where the size of the Pt colloids depends on the duration of chemical reduction. Computations of the high lying occupied and lowlying unoccupied orbitals indicated that Pt nanoparticles bind easily on both the Thymine (T) bases and the backbone in the PNA.

Within this study, a novel in-situ pretreatment is proposed theoretically and demonstrated experimentally, in which the formation of surface pits is subsequently stifled during thermal desorption. The proposed method involves fueling the well reviewed chemical oxide reduction reaction with a segregated source of material other than that ordinarily utilized in pit formation. The proposed method is implementable in virtually all deposition systems subject to the constraints of providing material deposition, substrate heating, and the creation of non-oxidizing environments either via vacuum or inert atmo sphere.

TiN/GaN multilayers with periods ranging from 5 nm to 50 nm were grown by reactive pulsed laser deposition (PLD) using elemental metal targets in an ammonia ambient at 20mtorr onto Si(100), MgO(100) and sapphire(0001) substrates. For growth on Si and MgO substrates, an epitaxial 40 nm thick TiN buffer layer was deposited prior to deposition of the multilayers. An epitaxial 150 nm GaN buffer layer was grown on sapphire substrates. For all substrates, layer thicknesses and periods investigated, x-ray diffraction and cross-sectional transmission electron microscopy revealed {0001} texture for GaN, and {111} texture for TiN in the multilayers. Both TiN layers and GaN layers thicker than ∼ 2nm appear to be continuous, with no evidence of agglomeration. Both phases are crystalline, with lateral grain sizes comparable to the layer thickness. These results suggest that epitaxy will not be necessary to fabricate pinhole free metal/semiconductor multilayers in the nitride system.

C-plane textured wurtzite AlN films deposited on both, 3C and 6H SiC as well as Si, have been employed in Pd/AlN/Semiconductor diode Hydrogen sensor structures. The SiC based devices behave as rectifiers and do not show the bias dependent capacitance expected for an MIS structure when reverse biased. The Si based devices, albeit exhibiting rectifying characteristics do show the expected dependence of capacitance on reverse bias, with typical depletion and inversion regions. The SiC based devices show the sensor response as change in bias voltage at constant forward current but the Si based device showed no response in this mode of operation albeit it did respond well in terms of the Hydrogen induces shift of the depletion capacitance vs. bias characteristic. As the AlN itself has the same structure in all cases, the differences in both, electrical characteristics and sensing response mechanism are related to differences in the AlN/Substrate heterojunction resulting from differences in the electronic band structure of the substrates.

In this paper we report the growth of GaAsSbN/GaAs single quantum well (SQW) heterostructures by molecular beam epitaxy (MBE) and their properties. A systematic study has been carried out to determine the effect of growth conditions, such as the source shutter opening sequence and substrate temperature, on the structural and optical properties of the layers. The substrate temperatures in the range of 450-470 °C were found to be optimal. Simultaneous opening of the source shutters (SS) resulted in N incorporation almost independent of substrate temperature and Sb incorporation higher at lower substrate temperatures.

The effects of ex-situ annealing in nitrogen ambient and in-situ annealing under As overpressure on the optical properties of the layers have also been investigated. A significant increase in photoluminescence (PL) intensity with reduced full width at half maxima (FWHM) in conjunction with a blue shift in the emission energy was observed on annealing the samples. In in-situ annealed samples, the PL line shapes were more symmetric and the temperature dependence of the PL peak energy indicated significant decrease in the exciton localization energy as exhibited by a less pronounced “S-shaped curve”. The “inverted S-shaped curve” observed in the temperature dependence of PL FWHM is also discussed. 1.61 μm emission with FWHM of 25 meV at 20K has been obtained in in-situ annealed GaAsSbN/GaAs SQW grown at 470 °C by SS.

The temperature and power dependence of Fermi-edge singularity (FES) in high-density two-dimensional electron gas, specific to pseudomorphic AlxGa1-xAs/InyGa1-yAs/GaAs heterostructures is studied by photoluminescence (PL). In all these structures, there are two prominent transitions E11 and E21 considered to be the result of electron-hole recombination from first and second electron sub-bands with that of first heavy-hole sub-band. FES is observed approximately 5 -10 meV below the E21 transition. At 4.2 K, FES appears as a lower energy shoulder to the E21 transition. The PL intensity of all the three transitions E11, FES and E21 grows linearly with excitation power. However, we observe anomalous behavior of FES with temperature. While PL intensity of E11 and E21 decrease with increasing temperature, FES transition becomes stronger initially and then quenches-off slowly (till 40K). Though it appears as a distinct peak at about 20 K, its maximum is around 7 - 13 K.

Good interfaces between electrodes and neural tissue are very important in chronic in vivo stimulation/recording. In order to study the effect of electrode materials and surface structure on neural interfaces, we cultured neurons on thin films of electrode materials that are expected to be biocompatible, such as platinum, and iridium oxide.

We used both flat film surfaces and laser micro-structured ones. The laser micro-structuring consisted of creating regular arrays of micro-bumps with height of about 1μm and diameter of 2-3 microns. We have found conditions for fabrication of such micro-bumps on platinum and iridium thin films on borosilicate glass substrate (Pyrex 7740) by mask-projection irradiation with single nano-second pulses from a KrF excimer laser (λ=248nm). Laser micro-structured iridium films were coated with IrO2 by pulsed DC reactive sputtering to obtain micro-structured IrO2 films. Two types of iridium oxide films were studied: amorphous (reactively sputtered at room substrate temperature) and polycrystalline (reactively sputtered at 300°C).

Cortical neurons isolated from rat embryo brain were cultured onto these thin film surfaces. Cells were more than 98% viable as determined by trypan blue exclusion tests. Poly-D-Lysine coated surfaces were used as positive controls for cell. Regular optical and fluorescent microscopy techniques were used to image the cells after they were cultured. To differentiate between live and dead cells a viability test with fluorescein diacetate (FDA) and propidium iodide was carried out. Also, immunocytochemistry analysis of neuron cells was performed using antibody for neuron-specific enolase (NSE) staining. A qualitative and quantitative comparison was carried out between the different types of modified electrode surfaces to study the neuronal growth in order to explore the feasibility of micro-bumps as stimulating/recording neural interfaces. These results are intended for use in optimization of future electrical stimulation/recording experiments that we plan to carry out.

Low-cost and chemical resistant microfluidic devices based on thermoplastic elastomers have been fabricated by hot embossing technology. Commercial available thermoplastic elastomer foils based on polyurethane (PU) in a thickness range of 100-600 μm have been used. Prior to the fabrication of the microfluidic devices the chemical resistance of the material against a wide range of standard biological buffer solutions and solvents had been analysed. We created systems of channels, reservoirs and holes for the connections to external capillaries by double-sided hot embossing with an alignment accuracy of +/- 3 micrometer. Closed channel structures were produced by an additional chemical bonding process of the embossed devices with another thermoplastic elastomer foil. The total volume of the fluidic cell was 2 μl/sensor for the use with SAW (surface-acoustic wave) sensor chip and about 0.2 μ/sensor for the impedance sensors. A novel multi-chamber fluidic device was successfully tested for in-situ immobilization of thrombin antibodies and Bovin Serum Albumin (BSA) on different sensor elements of the same sensor chip.

Nanostructures made of zinc oxide (ZnO), a wide-bandgap semiconductor, have recently attracted attention due to their proposed applications in low-voltage and short-wavelength (368 nm) electro-optical devices, transparent ultraviolet (UV) protection films, gas sensors, and varistors. Raman spectroscopy presents a powerful tool for identifying specific materials in complex structures and for extracting useful information on properties of nanoscale objects. At the same time the origin of Raman peak deviation from the bulk values is not always well understood for new material systems. There are three main mechanisms that can induce phonon shifts in the free-standing undoped ZnO nanostructures: (i) phonon confinement by the quantum dot boundaries; (ii) phonon localization on defects and (iii) the laser-induced heating in nanostructure ensembles. Here, we report results of the combined non-resonant and resonant Raman scattering studies of an ensemble of ZnO quantum dots with diameter 20 nm. Based on our experimental data, we have been able to identify the origin of the observed phonon frequency shifts. It has been found that the ultraviolet laser heating of the ensemble induces a large red shift of the phonon frequencies. It is calculated that the observed red shift of 14 cm-1 corresponds to the local temperature of the quantum dot ensemble of about 700°C.

A wide bandgap microcrystalline silicon film for the window layer of microcrystalline silicon thin film solar cells was obtained with very high frequency (VHF) glow discharge technology. The material was deposited on corning 7059 substrate at about 170 When H2/SiH4 was more than 100, Raman spectra showed that this material was highly crystallized, and no peak correlation with amorphous silicon was observed. This material showed strong n type before any intentional doping. We considered that the unintentional doping of oxygen and unpurified gases. The doping performance of this material was investigated by introducing B2H6 into the reacting gas. As increasing the rate of B2H6/SiH4 from zero to 0.5%, the conductivity changed from 10-1S.cm-1 (n type) to 10-8 S.cm-1 dramatically and than backed to 10-1 S.cm-1 (p type), which indicated that this material had excellent doping ability. Raman spectra also showed that the microstructure of these materials did not change obviously in this doping range. We gained the p-uc-Si:H film with thickness less than 30nm, and the conductivity was more than 10-2 S.cm-1, and crystalline volume fraction no less than 40%, the Egopt could be wider than 2.10eV. Using this p window layer in microcrystalline silicon solar cells with no ZnO rear reflection, the conversion efficiency was 8.30% (Voc=0.531V, Jsc=24.66mA/cm2, FF=63.41% ).

Microfabrication offers us the ability to fabricate numerous active devices at the micro-scale by patterning features on a variety of substrates for developing small devices in nanotechnology. Since materials scientists and chemists have been looking for unconventional approaches in the synthesis of novel materials, we introduce here a novel strategy of fabricating microfluidic reactors. A new microfluidic reactor was designed and fabricated for the microscale synthesis of materials, which has not been possible from conventional bulk syntheses. The microreactor presents a continuous, dynamic droplet generation. Using the microfluidic reactor, we demonstrate here a microfluidic synthesis of molecularly imprinted polymer (MIP), which is useful for bio- or chemical sensor applications due to its specific molecular recognition functions. Since the particle size of MIP's system directly affects their affinity capability in molecular recognitions, uniform MIPs’ particles at the nano- or micro-scale were produced via the microfluidic technique to achieve high sensitivity by developing ‘monoclonal’ MIPs particles, which have only high affinity binding sites.

A device with nanometric resolution in space and millisecond resolution in time, intended for neural electrophysiological imaging applications, is being developed and fabricated for in vitro experimentation. The device consists of (i) an integrated circuit (IC) platform and (ii) a carbon nanotube/polymethylmethacrylate composite construct. Arrays of equi-spaced multiple gold electrodes were fabricated using combined e-beam and optical lithography to achieve three types of IC platforms with three different scales of resolution. Carbon nanotubes were synthesized on silicon dioxide substrates using a chemical vapor deposition method. Subsequently, the carbon nanotube arrays were infiltrated with in situ polymerized polymethylmethacrylate to achieve electrical insulation between adjacent nanotube bundles. The composite construct was fabricated and exhibited electrical conductivity and connectivity between two faces of the composite along the length of the nanotubes. The carbon nanotube arrays grown on silicon dioxide exhibited uniform length and a high level of alignment, which was preserved subsequent the in situ polymerization process. The devices can be deployed as an interface between ICs and mammalian cells.

A Dual Beam Focused Ion Beam (FIB) machine has been used to deposit platinum contacts on different nanostructured materials using both electron- and ion-assisted deposition. The electrical quality of the deposited platinum has been studied, and the feasibility of using this nanofabrication method to extract electrical parameters of nanomaterials demonstrated. The advantage of combining electron- and ion-assisted deposition instead of using only ion-assisted deposition is discussed. The possibility of applying this method in the fabrication of future nanodevices is demonstrated in a gas nanosensor prototype.

We demonstrate that a multi-technology approach enables the accurate characterization of the thickness and optical properties of Amorphous Carbon (α-C) films used in semiconductor manufacturing. Because the material is found to be highly birefringent, with its measured refractive index and extinction coefficient depending strongly upon the polarization and angle-of-incidence of the optical probe beam that is used, conventional single angle-of-incidence Spectroscopic Ellipsometry (SE) has insufficient information-content to detect the ordinary and extraordinary refractive indices with sufficient accuracy. On the other hand, Beam Profile Reflectometry® (BPR®) is particularly strong in this case because it measures the actual reflectances for both polarization components (rather than just the difference between them) at multiple angles-of-incidence. Furthermore, the fact that BPR is a single-wavelength technique means that no assumptions must be made about the optical dispersion of the film and an absolute measurement can be made. It is then possible to combine this with other, spectral technologies to obtain ordinary and extraordinary n and k at all wavelengths. We show that, to first order, the birefringence can be modeled by assuming a single “anisotropy parameter”, the ratio between the ordinary and extraordinary refractive indices (or, more correctly, the complex dielectric functions). Using this approach in combination with a simple Bruggeman effective-medium dispersion model enables robust characterization of these films for production.

Electronic structures of several atomic wires of metals like Al, Ga and In on hydrogen passivated Si(001):1×1 surface have been examined in search of nanowires with metallic properties. The dihydrogenated Si(001) is patterned by depassivating only one row of Si atoms along the [110] direction. Various structures of adsorbed metals and their electronic properties have been studied. With our present effort it was observed that Al and Ga nanowire configurations with metallic property are unstable towards the formation of buckled metal dimers leading to semiconducting behaviour. However, indium atomic wire is close to the metallic limit and shows marginal preference for the formation of symmetric dimers. It is encouraging that In metallic wires on a patterned dihydrogenated Si(001) may be realized.

The basic principle for the operation of a thermally stimulated shape memory polymer (SMP) is a drastic change in elastic modulus above the glass transition temperature (Tg). This change from glassy modulus to rubbery modulus allows the material to be deformed above the Tg and retain the deformed shape when cooled below the Tg. The material will recover its original shape when heated above the Tg again. However, thermal activation is not the only possibility for a polymer to exhibit this shape memory effect or change of modulus. This paper discusses results of an alternative approach to SMP activation.

It is well known that the Tg of a thermosetting polymer is proportional to its crosslinking density. It is possible for the crosslinking density of a room temperature elastomer to be modified through photo-crosslinking special photo-reactive monomer groups incorporated into the material system in order to increase its Tg. Correspondingly, the modulus will be increased from the rubbery state to the glassy state. As a result, the material is transformed from an elastomer to a rigid glassy photoset, depending on the crosslinking density achieved during exposure to the proper wavelength of light. This crosslinking process is reversible by irradiation with a different wavelength, thus making it possible to produce light-activated SMP materials that could be deformed at room temperature, held in deformed shape by photo-irradiation using one wavelength, and recovered to the original shape by irradiation with a different wavelength.

In this work, monomers which contain photo-crosslinkable groups in addition to the primary polymerizable groups were synthesized. These monomers were formulated and cured with other monomers to form photo-responsive polymers. The mechanical properties of these materials, the kinetics, and the reversibility of the photo-activated shape memory effect were studied to demonstrate the effectiveness of using photo-irradiation to effect change in modulus (and thus shape memory effect).

Ni-nanowires are fabricated in a two-step electrochemical process. In the first step a porous silicon template with oriented pores perpendicular to the surface is produced. The electrochemical parameters for this etching procedure, like HF-concentration, current-density, etching-time and bath-temperature have to be chosen in a very small regime to obtain the favored structure in a good quality. This mesoporous silicon skeleton with highly oriented pores and homogeneous spatial distribution is filled in a further electrochemical step by a ferromagnetic metal, like Ni. This selforganized Ni-nanowire array is characterized by Auger-spectroscopy to evidence the loading of the pores over the full length. SEM and BSE are used to reveal the orientation of the pores and the homogeneous Ni-filling. By Fourier Transform image processing a predominant quadratic self-organized grouping of the (100) grown pores is identified. An additional investigation method is EDXS to show the element distribution in the sample. Furthermore magnetization measurements are used to generate a model for the Ni-loading in the channels. Not only wires but also granules in the size up to 200 nm are present. IR-spectroscopy investigations are used to compare the bare silicon wafer, the porous silicon (PS) sample and the PS with incorporated Ni at zero and finite magnetic fields.