Dye-sensitized solar cells composed of an n-doped ZnO nanowire array and a p-doped polymer layer appears to be a promising candidate for low-cost production of environment-friendly solar cells. In this work, we investigate hybrid devices consisting of a transparent conducting oxide (TCO) substrate, ZnO-nanowires (ZnO-NW) or a sol-gel prepared ZnO layer, a ruthenium dye (N719) and a PEDOT:PSS or P3HT layer. The dense polycrystalline ZnO layer is able to prevent short circuits, which have a strong effect on the performance of the solar cells. This is demonstrated by the use of only the ZnO layer which improves the open circuit voltage by a factor of 2 and the efficiency by a factor of 1.7 compared to cells with nanowires. That indicates that the system combined with a thin but dense ZnO layer and NW grown on it will show further improvement. Furthermore three different TCO substrates were investigated. Impedance spectroscopy (IS) reveals at least one additional Schottky barrier formed with ZnO:Al substrates. Spectral photovoltage measurements clearly show distinct absorption features correlated with the ZnO and N719 dye.

We report a novel application of Anisotropic Conductive Films (ACFs) technology to provide electrical contact and mechanical anchor between fracture transfer-printed (1-D) single crystal semiconductor micro- and nanopillars and a bottom metal. This fracture-transfer method enables highly crystalline micro- and nanopillars of different materials with diverse bandgaps and physical properties to be fabricated on appropriate mother substrates and transferred to form multilayered 3D stacks for multifunctional devices. The proposed protocol incorporates silver (Ag) nanoparticles into thermoplastic polymers exploitable in transfer-printed semiconductor devices and circuits with low contact resistance that is compatible with current IC processing methods. The vertical micropillars arrays are then embossed onto the polymer at its rubbery state by applying a vertical force leading to particle trapping between the bottom electrode and the micropillars. The polymer is then hardened while retaining the applied vertical force. By applying a lateral force on the mother substrate, the firmly cemented pillars are fractured off thereby allowing the mother substrate to be reused.

Methods for extracting or harvesting energy from the surrounding battlefield environment are of great importance to the United States Army. Scavenging energy from local environments reduces the required energy and weight transported to the theater. Micro- and nano-scale metal-insulator-metal (MIM) tunnel diodes are being developed to provide half-wave rectification as part of a “rectenna” energy harvesting system, which includes a radiation-collecting antenna, a rectifying MIM tunnel diode, and a storage capacitor. In this work, high-frequency MIM tunnel diodes for power rectification were designed, fabricated and characterized. Planar Pt/TiO2/Ti stacks are being fabricated to create a diode with highly asymmetric I-V characteristics that has a very low threshold voltage. The metals were chosen for their high work function difference, and the insulator was chosen for its barrier height, its compatibility with Ti, and its availability. The energy band diagram and the I-V characteristics were modeled to determine the feasibility of the Pt/TiO2/Ti material system for use as a rectifier diode in a rectenna system. Metals and insulator thin films were deposited onto silicon dioxide/silicon substrates. Pillars with lateral dimensions ranging from 20 μm x 20 μm up to 100 μm x 100 μm were fabricated. The dielectric thickness of the MIM diode was varied from 5 nm up to 50 nm to determine the optimal thickness for quantum tunneling. I-V measurements were taken using an electrical characterization system to confirm a non-linear, asymmetric response on a survey of devices fabricated with varying areas. Preliminary results exhibit asymmetric I-V characteristics with threshold voltages of less than 700 mV.

Fabrication of dielectric thin films using dispersions of ultra-small ZrO2 and BaTiO3 nanoparticles with a low-temperature processing is reported. Highly crystalline and monodisperse cubic-ZrO2 and tetragonal-BaTiO3 nanoparticles were synthesized using non-aqueous approach. Post synthesis, nanoparticle dispersions were realized through chemical modification of their surface. The obtained dispersions were then employed for the fabrication of homogeneous and densely-packed dielectric thin films, verified through scanning electron microscopy.

We report simple and effective methods to develop long-term, stable silicon nanowire-based pH sensors and systematic studies of the performance of the developed sensors. In this work, we fabricate silicon nanowire pH sensors based on top-down fabrication processes such as E-beam lithography and conventional photolithography. In order to improve the stability of the sensor performance, the sensors are coated with a passivation layer (silicon nitride) for effective electrical insulation and ion-blocking. The stability, the pH sensitivity, and the repeatability of the sensor response are critically analyzed with regard to the physics of sensing interface between sample liquid and the sensing surface. The studies verify that the sensor with a passivation layer over critical thickness show long-term, stable sensor response without long-term drift. The studies also show the detection of pH level with silicon nanowire sensors is repeatable only after proper rinsing of sensor surfaces and there exists trade-off between the stability and the pH sensitivity of sensor response.

The titanium dioxide (TiO2) nanoparticle (NP) structure has higher surface area and dye loading value to increase photon absorption while the nanotube (NT) can suppress the random walk phenomena to enhance carrier collection. In this work, hydrothermal method was utilized to infiltrate the TiO2 nanotube array by TiO2 nanoparticles with the aim of combining the advantages of both nanostructures to improve dye sensitized solar cells (DSSCs) efficiency. Structure morphology, device performance, and electrochemical properties were investigated. SEM observation confirmed that around 10 nm TiO2 nanoparticles uniformly covered the NT wall. TiO2 NT samples at three different lengths: 8 μm, 13 μm and 20 μm, decorated with different amount of nanoparticles were studied to optimize the structure for light absorption and electron transport to achieve high solar conversion efficiency. Electrochemical impedance spectroscopy (EIS) was also employed to investigate the cells’ parameters: electron lifetime (τ), diffusion length (Ln) et al, to gain insight on the device performance. The incident photon conversion efficiency (IPCE) was also reported.

We develop a novel patterning technique to create 3D patterns of micro, nanoparticle assembly via evaporative self-assembly based on confinement/release of micro/nano particles assembly based on the coffee-ring effect of evaporating suspension. Based on the presented technique, we demonstrate that the patterns of 3D assembly of various sizes of microparticles (Silica), metal oxide nanoparticles (TiO2, ZnO) and metallic nanoparticles (Ag) can be successfully generated by low-concentrated particle suspension (1.25 wt % ~ 5 wt %) without additional sintering steps and we also show the geometries of the patterns can be finely controlled by adjusting the parameters of the process.

Carbon-based materials like nanotubes and graphene are heavily investigated as future transistor devices and in interconnect applications. While much of the interest has been devoted to the device aspects in competition to conventional transistors, the paper here will focus on some less known applications of pyrolytically deposited carbon. Proposed and demonstrated are applications in capacitors, gate materials, through-silicon vias, novel non-volatile memories, carbon-silicon Schottky diodes and sensors.

Graphene, two-dimensional layers of sp2-bonded carbon, has many unique properties. In this paper, graphene is decorated with flower-like MnO2 nanostructures for the application in energy storage devices. The as-prepared graphene and MnO2 nano-flowers, which were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), were assembled into an asymmetric supercapacitor. The specific capacitance of the graphene electrode reached 245 F/g at a charging current of 1 mA. The MnO2 nano-flowers which consisted of tiny rods with a diameter of less than 10 nm were coated onto the graphene electrodes by electrodeposition. The specific capacitance after the MnO2 deposition is 328 F/g at the charging current of 1 mA with an energy density of 11.4Wh/kg and power density of 25.8 kW/kg. This work suggests that our graphene-based electrodes can be a promising candidate for high-performance energy storage devices.

We have developed material (Bi0.7Dy0.3FeO3)(BDFO) which exhibits the multiferroic behavior at room temperature with significant coupling in bulk as well as thin films. If these properties could be fashioned in nano rods, implementation in devices could be certainly more prominent and straight forward. We have therefore used vertically aligned arrays of silicon rods (~5 μm in length and ~ 500 nm in diameter) as base material to direct the growth of BDFO in rod form. BDFO is deposited on the surface of Si rods by using pulsed laser deposition technique. These BDFO/Si rods are then separated from the support, dispersed into propanol and transferred onto SiO2/Si substrates for testing. X-ray diffraction (XRD) results indicate presence of phase pure BDFO layer on Si rods. Saturation observed at room temperature in magnetic and ferroelectric hysteresis loops confirm the coexistence of ferromagnetic and ferroelectric properties. Change in ferroelectric polarization measured on single rod in the presence of applied magnetic field suggests the coupling behavior between two order parameters. Moreover, change in magnetic domain pattern of BDFO rods associated with applied electric field further supports the presence of coupling behavior in both ways. The vertical and lateral displacement occurring in BDFO/Si rods with applied electric field helps to confirm their piezoresponce behavior. BDFO/Si nanorods with multifunctional properties could find variety of novel device applications with flexibility and simplicity in operation. It might include single rod power generation by means of applied stress or magnetic field.

In this paper, we demonstrate a heterogeneous integration technique that preserves the integrity, order, shape, and fidelity of vertically aligned single-crystal semiconductor micro- and nano- pillars by harvesting and transferring them from a single crystal substrate to a low-cost carrier substrate. The mechanism of the transfer technique exploits a combination of vertical embossing and lateral fracturing of the crystalline pillars with the assistance of a spin-coated polymer layer on a carrier substrate as well as facilitating multilayer process device integration. Specifically, the novel use of a water soluble adhesive polymer from MasterBond that acts simultaneously as a mechanical transfer polymer and as a sacrificial harvest layer further expands the versatility of this approach. Arrays of vertical micropillars of average height ~15)μm and diameter ~1.5μm on a die silicon substrate of 5mm x 5mm were fabricated via transformative top-down approaches (DRIE) on a single crystal silicon substrate and then transferred to a different target carrier substrate using the adhesive polymer assisted bendingfracturing process. The adhesive polymer is odorless, non-conducting, easy to process, spincoatable, optically transparent, resistant to heat, high mechanical strength and easily cures at room temperature. The original pillar wafers may be used repeatedly after polishing for generating more devices and are minimally consumed. Low contact resistances are formed for electrical addressing using metals and conducting thermoplastics of Ag nanoparticles. This heterogeneous integration technique potentially offers enhanced photon semiconductor interactions, while enabling multimaterial integration such as silicon with compound semiconductors (InP, GaAs etc.) for applications, including high speed electronics, low-cost and flexible electronics, displays, tactile sensors, and energy conversion systems.

Anodized Aluminum Oxide (AAO) based micro-channel plates (MCP) are fabricated in order to develop economical large-area photodetectors. Commercially available glass capillary array has a limitation to reach channel diameter below ~10 microns. However, smaller channel diameter is desired for better spatial and fast timing resolution. AAO based MCP is a good candidate to produce channel diameter less than 10 um by taking advantage of the nano-scale intrinsic pores during etching process. In this study, various channel diameters are fabricated with use of lithographic patterning techniques and wet etching; and characterized with optical, atomic force, and scanning electron microscopies. The channel diameter, channel length and related aspect ratio, as well as the open area are varied in order to maximize the MCP photon amplification.

Large-scale graphene sheets were grown on thin nickel film coated Si substrates using a reliable and repeatable thermal Chemical Vapor Deposition (CVD) technique. The graphene films were then transferred onto a SiO2 coated Si wafer to fabricate a 5 mm x 5 mm resistive sensor structure. Raman spectroscopy analysis confirmed the existence of graphene. Preliminary sensing results were demonstrated by the detection of hazardous gases such as NO2 and MMH (mono-methyl hydrazine). Characterization of the device channel resistivity (switching response) was conducted as a function of the analyte type and concentration. The sensor response indicates a charge transfer mechanism between the analytes and graphene.

In recent years, an increase in usage of methane gas in household and automobile industry has been observed. Detection of methane is always a great cause of concern for safety at home or automobile industries, productions in mines and chemical factories. This paper reports the response characteristics of rf-sputtered SnO2 thin films (90 nm thin) loaded with nanoscale catalytic clusters for detection of methane. Ultrathin (8 nm) metal and metal-oxide catalysts (Pt, Ag, Ni, Pd, Au, NiO, Au2O3) clusters are loaded over the surface SnO2 thin film. The SnO2-Pd cluster structure is found to exhibit an enhanced response (97.2%) for 200 ppm of methane at a relatively low operating temperature (220oC). The enhanced response is shown to be primarily due to the dominant roles played by both Fermi level energy control mechanism and spillover mechanism.

Light trapping is one of the key challenges for the next generation of thin film solar cells. In this work, we have identified the distinct light trapping effects for short and long wavelength solar spectrum ranges, by investigating lighting trapping structures on both sides of Si thin film solar cells. The sub-wavelength moth-eye-like photonic front surface and multi-layer grating photonic crystal reflector on the bottom surface are studied in detail via the Finite Difference Time Domain method for its solar energy absorption characteristics. Our study reveals the drastic difference in the light trapping effects within the solar spectrum wavelength. This work may provide guidance for efficiency enhancement of next generation thin film photovoltaic cells.

The Cu-based film catalysts with various additive metals have been successfully prepared by the electroless plating on ZnO nanorods/stainless steel substrates. The microstructure features of the Cu-based films are highly porous and composed of plate-type grains. The addition of zirconium, aluminum, and iron into Cu-based film catalyst can improve the activity and the stability of the film catalysts. The catalytic durability of the Cu-based film catalysts has also been improved by addition of Zr, Al, and Fe into Cu-based films. This is attributed to the formation of the stable ZrO2, Al2O3, and Fe2O3 nanoparticles with good dispersion in the films.

Homogeneous composite thin films of Fe2O3-carbon nanotube were synthesized in a novel, single-step process by metalorganic chemical vapor deposition (MOCVD) using ferric acetyl acetonate as precursor. The deposition of composite takes place in a narrow range of CVD conditions, beyond which the deposition either multiwall carbon nanotubes (MWNTs) only or hematite (α-Fe2O3) only takes place. The composite film formed on stainless steel substrates were tested for their supercapacitive properties in various aqueous electrolytes.

We report a novel concept for the direct integration of capacitors in printed circuit boards using ultra-small BaTiO3 and ZrO2 nanoparticles prepared by a chemical method. Electrical properties comparable to surface mount ceramic capacitors were achieved by proper processing of the nanoparticles, achieving a device-yield of >90% under research environment. The loss factor of the presented integrated capacitors does not exceed 0.05 independent of frequency, capacitor’s electrode area or applied bias voltage.

Performance on dye-sensitized solar cells (DSCs) using a titanium dioxide nanoparticle layer treated by tetrafluoromethane gas plasma was investigated through electrical properties under illumination. A 50%-increase of maximum power density was observed in the plasmatreated DSCs when RF power and processing time are 1W and 100s, respectively. We also obtain diode factor between 1 and 2 in the fabricated DSCs from a plot of short-circuit current versus open-circuit voltage and then the calculated current density-voltage curve was good agreement with the experimental data.