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A high-speed optical humidity sensor was fabricated from a nanostructured titanium dioxide thin film. A refractive index depth profile designed to yield a narrow-bandpass optical interference filter was obtained through nanoscale porosity variations produced by a physical vapor deposition technique known as glancing angle deposition (GLAD). The GLAD process provides film morphology control on the 10 nm scale through a combination of deposition at highly oblique vapor incidence angles and controlled substrate motion. Under varying humidity conditions the transmittance spectrum of the filter shifts due to effective index changes of the porous structure resulting from water vapor adsorption/desorption. Performance analysis has shown that this device is highly sensitive, exhibits minimal hysteresis, and is extremely fast. The adsorption and desorption response times were measured to be 270 ms and 160 ms, respectively.

Electrochemical oxidation of Mn thin films produces a highly capacitive, porous MnO 2 surface layer. The effects of current density and deposited Mn layer thickness on the morphology of the porous surface layer are quite pronounced. A higher current density results in a much thinner, finer porous layer while thicker deposited Mn films give much thicker porous films. Increasing the current density results in a film with greater hydration and an increase in capacitance. For the films of varying deposited layer thickness, oxidation occurs at a single current density and, as a result, the relative hydration of the film does not change noticeably. Increasing the deposited layer thickness results in a porous surface layer that increases in thickness, but with a constant amount of hydration. This combination of trends results in a significant increase in the areal capacitance of the film but little change in the specific capacitance.

The mechanical behavior of a helically perforated thin film structure was simulated by finite element analysis. The validity of the results was confirmed by comparison to a nanoindentation measurement performed on a nickel helically perforated thin film sample. It was found that variation of the helical pitch angle from 35° to 70° resulted in a change of 1.5 times in the elastic modulus. Since the fabrication process used to create the actual samples allows for variation of the pitch angle, this result may enable the tailoring of materials for use in micro- and nanoscale devices.

Capacitive-based humidity sensors were fabricated using unique nanostructured aluminum-oxide thin films. These sensors exhibited extremely fast desorption response times as short as 42 ms. In this paper, we present the effects of varying the thin-film porosity on sensor performance. Specifically, we look at the capacitive response and the desorption response time of the sensors. It was found that increased porosity tends to decrease the desorption response time and increase the relative humidity where the devices become sensitive.

An enhancement of the glancing angle deposition (GLAD) technique called PhiSweep was used to grow slanted columns of silicon and titanium dioxide onto patterned substrates. The PhiSweep technique involves periodically rotating the substrate back and forth during the deposition process, which reduces column fanning caused by anisotropy in the shadowing conditions. The patterned substrates consisted of a tetragonal array of hillocks with 100, 200, and 300 nm periodicities and were fabricated using electron beam lithography. The PhiSweep method alters the tilt angle of the slanted columns compared with those grown using traditional GLAD. We present a derivation of the tilt angle of the slanted columns as a function of the parameters of the PhiSweep technique. The tilt angles of the silicon and titanium dioxide films were measured and agree with the predicted values. The films fabricated using the PhiSweep method are compared with similar films grown using traditional GLAD. The PhiSweep technique produced films with substantially less column fanning than those grown by traditional GLAD. This reduction in column fanning has extended the size range over which periodic GLAD structures, such as square spiral photonic crystals, can be grown.

Highly porous thin films with columnar microstructures are applicable to many optical, chemical, and electronic devices, and can be fabricated using the glancing angle deposition method for physical vapour deposition onto tilted substrates. In a recent advancement of this method, it was shown that decoupling of the vapour incidence direction from the column growth direction provides significant flexibility to engineer the pore structure of the films. Here we elaborate on the decoupling principle by applying it to chiral thin films with a periodic microstructure, and demonstrating how it leads to improved film uniformity and the elimination of column broadening. We also show the effects of such depositions onto substrate seed layers with intentional defects. Substrate based defects normally transfer to thin films as air filled defects, but here we present for the first time that a simple adjustment of the deposition parameters can invert the normally air filled defects to become solid, evaporant filled defects. This defect engineering capability provides new opportunities for the deployment of glancing angle deposition thin films to photonic bandgap crystals and microfluidic devices.

Nanostructured photoluminescent thin films of europium-doped yttrium oxide (Y2O3:Eu), a well-known luminescent material, were grown using electron-beam evaporation in combination with the glancing-angle deposition technique. GLAD makes use of controlled substrate motion during extremely oblique physical vapor deposition of a thin film resulting in a high degree of control over the nanostructure of the film. Scanning electron microscopy and x-ray diffraction were used to characterize film nanostructure, while the light emission properties of these films were characterized by photoluminescence measurements. Transmission ellipsometry measurements were used to determine the degree of selective transmission of polarized light through the samples. The polarization of the emission from chevronic and helical films was determined through the measurement of the Stokes parameters of the emitted light for each sample. Comparison of the degree of polarization during the emission experiments to the degree of selective ...

We present a new method for making functional patterns in thin films consisting of highly ordered arrays of complex, submicrometer structures, deposited at oblique flux incidence angles using the glancing angle deposition technique. By performing physical vapor deposition on direct write seed layers with intentional point and line lattice defects, we are able to generate embedded air-filled linear and planar patterns in the films in a single-step transfer approach with no need for conventional postdeposition micromachining. The uniformity and porosity of the thin films is fully maintained, with minimal impact on the film morphology adjacent to the patterns. This ability to engineer air-filled patterns is crucial to several promising thin-film applications, including photonic band gap crystals and microfluidics.

An in-depth study of the oxidation step required to produce electrochemical capacitors from porous manganese-oxide materials was carried out. The oxidation process takes place under the application of a small anodic current in a solution of 1 M Na2SO4, resulting in the formation of a three-layered structure. During the oxidation process, a base layer of undisturbed zigzag material oxidizes from Mn/MnO to Mn3O4. At the same time, a second layer forms directly on the surface of the zigzag material. The layer is partly crystalline Mn3O4 and partly amorphous. The final and most important layer is the amorphous, hydrated MnO2 surface film. It is believed that this layer is solely responsible for the capacitive behavior of these films. The porosity of the electrode prior to oxidation is shown to be immaterial as oxidation of a fully dense film results in similarly high capacitive values attributed to the formation of a porous surface layer.

Titanium dioxide is a material of interest for optically active structured films due to its high index of refraction and transparency across the visible wavelength range. A variety of films, consisting of different structures, were deposited by reactive electron beam evaporation using the glancing angle deposition process. Samples of these films were annealed at 500 °C for 3 hours in air. The structures of both as-deposited and annealed films were examined by scanning electron microscopy, X-ray diffractometry, and transmission electron microscopy. It was found that as-deposited films were amorphous with a very fine structure. The annealed films were found to be polycrystalline anatase and had lost their fine structure. In addition, the optical properties of the films were examined by spectrophotometric transmission measurements, wherein it was found that the annealing caused a significant transmission increase across the visible spectrum.

We report the fabrication and optical characterization of a tetragonal square spiral photonic crystal with a three-dimensional relative band gap of approximately 10% using the glancing angle deposition (GLAD) technique. This thin film structure is produced in a one-step process that is highly versatile as a wide range of crystal structures can be created simply through the variation of deposition parameters. Measurements indicate upper and lower frequency band edges at vacuum wavelengths of 2.50 and 2.75 μm, in the infrared region of the spectrum.

Recent experimental work by a number of researchers has demonstrated that unusual high porosity thin films may be obtained in physical deposition systems by combining glancing angle deposition with in situ substrate motion control. The microstructure of these films consists of isolated columns engineered into shapes such as helices, posts, or chevrons. Due to the isolated nature of the columns, the films present a unique opportunity to study fundamental thin film growth behavior and, in particular, the influence of the self-shadowing mechanism in three dimensions. Apart from this academic motivation, there is the need to characterize the physical constraints imposed on the engineering of these films. In particular, this study will have implications for the realization of isolated, periodically arranged nanostructures envisioned for certain applications such as photonic band gap crystals. Results from an ongoing study of growth dynamics, morphology, porosity, and scaling behavior, and the dependence of these features on deposition parameters are presented.

Arrays of self-sealed structures have been grown on silicon mesas and lines, which consist of porous thin film centres enclosed by solid borders, and can be fabricated in a single step using a unique method of film growth called glancing angle deposition (GLAD). These specialized structures may have potential for use in microreactor, microfluidic, chromatographic, nano-assay, lab-on-a-chip, biochemical, and other related applications.

We investigated the use of a novel class of porous thin films for the characterization of tapping mode atomic force microscope (AFM) tips. Chromium and titanium films were evaporated using the technique of glancing angle deposition (GLAD) onto rotating silicon substrates. The morphology of the resulting films consisted of isolated vertical posts of sub-micron size. These isolated topographical features are small enough to provide useful information about tip morphology and aid in assessing tip wear and damage. The films were imaged using an AFM, and previously published tip reconstruction algorithms were used to obtain three-dimensional tip functions. These compared well with envelope profiles determined from scanning electron microscope images of the tips.

Efficient and rapid adsorption of microperoxidase 11 within a highly porous ITO thin film (200 nm) prepared by glancing angle deposition was achieved. Adsorbed redox molecules were reversibly and rapidly reduced throughout the 3D-conductive matrix in ca. 50 ms, allowing the heterogeneous electron transfer rate to be determined by derivative cyclic voltabsorptometry. © 2011 The Royal Society of Chemistry.

Branch growth is directed along two, three, or four in-plane directions in vertically aligned nanowire arrays using vapor-liquid-solid glancing angle deposition (VLS-GLAD) flux engineering. In this work, a dynamically controlled collimated vapor flux guides branch placement during the self-catalyzed epitaxial growth of branched indium tin oxide nanowire arrays. The flux is positioned to grow branches on select nanowire facets, enabling fabrication of aligned nanotree arrays with L-, T-, or X-branching. In addition, a flux motion algorithm is designed to selectively elongate branches along one in-plane axis. Nanotrees are found to be aligned across large areas by X-ray diffraction pole figure analysis and through branch length and orientation measurements collected over 140 μm2 from scanning electron microscopy images for each array. The pathway to guided assembly of nanowire architectures with controlled interconnectivity in three-dimensions using VLS-GLAD is discussed. © 2014 American Chemical Society.

UV-visible absorption spectroelectrochemistry elucidated the different redox behaviours of Fe(III)- and Co(III)-mimochrome VI artificial enzymes, adsorbed on mesoporous conductive films of ITO. The reduction of the ferric complex was rapid and reversible, while the cobaltic complex exhibited irreversible processes probably related to multiple coordination states.

Porous thin films with unique microstructures have been fabricated with the glancing angle deposition technique. This technique utilizes highly oblique deposition angles to make use of initial growth and shadowing conditions, which allow thin films consisting of microsprings and arrays of microcantilevers to be engineered with nanometre scale control. The mechanical properties of these microstructured films were studied with a nanoindentation technique. Several microscopic `springbed' films were tested over a range of forces using a spherical indenter tip. The geometries of the microsprings were varied, and a number of different materials were used to fabricate these films, which were typically a few micrometres thick. Slanted post arrays, resembling microscopic cantilevers, were also subjected to nanoindentation tests. The results of initial experiments and theory show that these microstructures behave in a manner analogous to macroscopic springs and cantilevers, and may offer opportunities for application as resonator devices.

Simulations of the flow of heat through porous thin films by the three-dimensional microstructural thin film simulation framework 3D-Films are discussed in this paper. For each simulation, the film structures are generated by the thin film growth model 3D-Films and then used to generate a finite difference based thermal model by the program 3D-Films/Thermal. This program creates a block based data structure using a 3D quadtree mesh and subsequently solves for the steady state heat flow through the film structure. In this paper the film growth and thermal models are used to analyze and suggest optimization of porous thermal barrier coatings produced by glancing angle deposition techniques. The paper also deals with the determination of the accuracy and efficiency of the thermal model. Studies on the effect of reducing the resolution of the simulated film for less memory intensive thermal simulations are presented, indicating that a reduction of the resolution by a factor of 3 and the number of solution variables by as much as a factor of 27 is feasible. The simulations Of ZrO2 thermal barriers are compared to experimental results with a relatively close match being obtained. Finally, the simulator is used to analyze the effectiveness of a number of potential thermal barrier structures produced by glancing angle deposition techniques. These results suggest that the most effective thermal barrier film microstructures will be porous films consisting of slanted posts or large pitch helices.

Electron field emission was measured from carbon and silicon thin films comprised of a porous, pillar microstructure fabricated by the glancing angle deposition technique. This single step glancing angle deposition technique leads to a high areal density of pillars with nanometer-scale diameters. A comparison of emission has been made against normal dense films of the same material. It has been observed that emission from the pillar films occurs at a much lower threshold voltage than emission from the normally deposited film.

A new approach is described in the deposition of thin films for thermal barrier applications. Using controlled substrate motion, porous layers and capping layers were vacuum deposited in an alternating fashion, creating a new, multilayered film structure. Direct measurements of the thermal properties of these multilayers were made using the 3ω and Mirage techniques. In the 3ω technique, heat is introduced into the coating by an AC current flowing through an evaporated resistor with a frequency ω. A fit of resistor voltage as a function of frequency yields the thermal conductivity. In the Mirage technique, an oscillating temperature is induced immediately above the film using a pulsed laser. A second probe laser aligned parallel to the surface is deflected by these temperature variations, and the thermal diffusivity is then found by fitting amplitude and phase shift data to the solution of the three-dimensional diffusion equation. Typically, the 3ω and Mirage techniques measure thermal constants in directions normal and parallel to the substrate, respectively. Measurements using these methods led to estimates of a reduction in thermal diffusivity of as little as 9% of that of films deposited entirely at normal incidence. Thermal simulations of similar structures also predicted a substantial decrease in overall thermal conductivity. In a specific case, an improved conductivity of 18% of that of films deposited by standard techniques was estimated.

An advanced deposition technique known as glancing angle deposition (GLAD) [K. Robbie, J. C. Sit, and M. J. Brett, J. Vac. Sci. Technol. B 16, 1115 (1998); K. Robbie and M. J. Brett, U.S. Patent No. 5,866,204 (filed 1999)] has been used to fabricate periodic arrays of magnetic pillars and randomly seeded magnetic helices, posts, and chevrons. Because of the nature of initial film nucleation, the GLAD process normally distributes posts randomly on the substrate surface. We can grow periodic arrays of GLAD microstructures by suppressing the randomness inherent within the initial nucleation stage of film growth. Shadowing sites were fabricated by pre-patterning a thin titanium layer on silicon substrates into a square array using electron beam lithography. These sites shadow regions of the substrate from incident flux during film deposition and act as preferred nucleation sites for film growth. Using this process, we have fabricated periodic arrays of cobalt posts with a regular elemental period of 600 nm and post diameters and heights of 300 and 400 nm, respectively. Randomly seeded posts, helices, and chevrons were also fabricated. The mean separation for the randomly seeded posts was 350 nm with individual post diameters of 100�150 nm, while the separations for the helices and chevrons were less than 100 nm. X-ray diffraction, transmission electron microscopy, and a dc superconducting quantum interference device magnetometer were used to analyze the magnetic and crystal properties of both the periodic and randomly seeded arrays. A newly developed three-dimensional ballistic deposition simulator was used to simulate the growth of the periodic post arrays in order to better understand the growth mechanisms., 46th National Symposium of the American Vacuum Society

Porous thin films with engineered microstructures have been fabricated using glancing angle deposition (GLAD). GLAD films with chiral microstructures have been previously shown to exhibit unique chiral optical response. The pores of these films were embedded with (non-chiral) nematic liquid crystals (LCs) to produce a new composite optical material wherein the GLAD film induces chiral nematic-like LC orientation. We demonstrate here reversible electro-optic switching of the LC component of these hybrid films. Unaddressed, cells of GLAD/LC hybrid films show enhanced chiral optic response compared with the unfilled GLAD film. When addressed, the chiral optic response vanishes.

The one-dimensional collisionless sheath model of electropositive plasmas is extended here to study the sheath structure of an electronegative plasma at steady state with the assumptions of cold positive ions and planar sheath configurations. Similar to the electropositive plasma sheath, a net charge layer is built within the sheath. However, the net charge density distribution within the sheath is sensitive to the plasma electronegativity (ratio of negative ion density n/sub -b/ to the electron density n/sub cb/). It is most interesting that the sheath thickness varies nonmonotonically with the plasma electronegativity of the bulk plasma. Last, the effects of applied wall potential and temperature ratio of electrons to negative ions are discussed.

The Druyvesteyn distribution function, an example of a non-Maxwellian distribution for electrons, is used to study the effects of electron energy distribution functions (EEDFs) on the floating potential of an isolated particle under thin plasma sheath conditions by comparing the results with a Maxwellian distribution, and an analytical expression xfD2(xfM)1/2 is obtained, where xfD and xfM are the normalized floating potentials with Druyvesteyn and Maxwellian electron distributions, respectively. Finally, the results are extended to a whole family of EEDFs with the functional form f() = Ap1/2exp(-Bpp), where p is an arbitrary number p1.

Pulsed laser deposition (PLD) has been used together with the Glancing Angle Deposition (GLAD) technique [1,2] for the first time to produce highly porous structured films. A laser produced carbon plasma and vapour plume was deposited at a highly oblique incident angle onto rotating Si substrates, resulting in films exhibiting high bulk porosity and controlled columnar microstructure. By varying the substrate rotation rate, the shape of the microcolumns can be tailored. These results extend the versatility of the GLAD process to materials not readily deposited by means of traditional physical vapour deposition techniques.

The reliable and complete filling of vias and trenches with an appropriate metal is an important process in the fabrication of microelectronic components. Due to its favorable electronic properties and its reliability, copper is a common choice for replacing aluminum as a metallization material. One metallization procedure of interest is the sputter reflow of copper. The sputter reflow process begins with depositing copper via traditional sputter technologies. The films are subsequently made to fill micrometer and submicrometer trenches and vias through surface diffusion enhanced by annealing. This paper studies fundamental considerations such as deposition rates, underlayer material, and transport mechanisms through numerical simulation using the process simulators SIMSPUD and GROFILMS. The simulations are further used to study via filling using Cu reflow and alternative methods including in situ annealing, three-step deposition, and a four-stage deposition-chemical mechanical polishing procedure. Simulation results are presented as depictions of the film on the feature scale. A discussion of the algorithmic solutions to the three-dimensional problems associated with vias is also provided.

The development and optimization of sputtering techniques for the deposition of refractory metal thin films for very large scale integration (VLSI) barrier and encapsulation layers is of significant concern for the microelectronic fabrication industry. A number of directed sputtering techniques such as collimation and low pressure longthrow configurations have been applied to this problem. This paper addresses a number of issues present in the understanding and simulation of the growth of films deposited by directed sputtering techniques over VLSI topography. In particular the role of high energy neutral gas atoms reflected from the target is investigated as a source of resputtering. Also addressed is the creation of a low density porous film on the sidewalls of vias/contacts due to oblique incident fluxes on these areas. Experimentally Ti and W films are deposited at pressures varying from 0.2 to 12.0 mTorr with and without collimators present. A number of re-emission/resputtering mechanisms were investigated using a Monte Carlo growth simulator and it was found that the model most consistent with the experimental films was an assumption of resputtering due to reflected neutrals. A significant result is a dramatic increase in the resputtering rate when a collimator was present due to a relative increase in the reflected neutral flux. Finally, the paper presents an analysis of the effect of pressure on bottom and step coverage in high aspect topography.The development and optimization of sputtering techniques for the deposition of refractory metal thin films for very large scale integration (VLSI) barrier and encapsulation layers is of significant concern for the microelectronic fabrication industry. A number of directed sputtering techniques such as collimation and low pressure longthrow configurations have been applied to this problem. This paper addresses a number of issues present in the understanding and simulation of the growth of films deposited by directed sputtering techniques over VLSI topography. In particular the role of high energy neutral gas atoms reflected from the target is investigated as a source of resputtering. Also addressed is the creation of a low density porous film on the sidewalls of vias/contacts due to oblique incident fluxes on these areas. Experimentally Ti and W films are deposited at pressures varying from 0.2 to 12.0 mTorr with and without collimators present. A number of re-emission/resputtering mechanisms were investi...

Modified sputtering techniques, such as long throw sputtering, collimation, and ionized sputtering, have been proposed to improve VLSI topography bottom coverage by narrowing the angular distribution of the sputter flux at the substrate and reducing subsequent flux shadowing at the bottom of topography. This paper first investigates a number of unique aspects involved in the simulation of long throw sputter systems. In particular, time importance of inhomogeneous film density and nonunity sticking coefficients are addressed. The second part of the paper presents a simulation study of long throw sputtering, providing a comparison to collimated and standard sputtering systems. The simulations are performed using the SIMSPUD/SIMBAD ballistic deposition tool. SIMSPUD is used to study film uniformity over a 300-mm wafer and to generate angular distributions at the center and edge of the wafer. The ability of SIMBAD to simulate directed sputtering systems is verified by direct comparison to Ti films deposited into oxide trenches. The importance of modeling the film microstructure is demonstrated by comparison between cross-sectional SEM's micrograph for evaporation and modeling results, such as long throw sputtering with a variety of substrate/target spacings, typical "standard" as well as "collimated" systems. SEM's of overhang structures and simulations are also presented to demonstrate nonunity sticking during the co-sputtering of TiW.

The temperature cycling effect on electromigration behavior under pulsed current conditions for metallization used in very large scale integrated (VLSI) devices is numerically investigated. This involves the solution of a two-dimensional (2-D) heat-conduction equation and a one-dimensional (1-D) diffusion-drift equation. We find that the characteristic thermal response time for establishing the equilibrium, for a typical VLSI metallization structure, is slightly longer than 1 ms. As a result, the steady-state temperature difference in the metal line between the upper and lower values in response to the pulsed current operation is maximized when the frequency is below 250 Hz with a duty factor of 0.5. The temperature difference decreases with increasing frequency. At frequencies above 10 MHz, the thermal capacity of the metal line inhibits appreciable temperature fluctuation. For a constant line temperature the time-dependent vacancy buildup has been shown to be proportional to /spl tau//sup m/ with m=2 (where /spl tau/ is the duty factor), consistent with the "average model" for predicting the failure time. In this study, we confirm the speculation that Joule heating due to an elevated current density employed in accelerated life testing can bring about an m

We have fabricated and characterized thin films of WSiX in order to produce highly resistive films (about 1 kΩ/sq), with temperature coefficients of resistivity (TCR) less than 0.2%/K, by a technique which, in our experience, is more reproducible, and has better uniformity than comparable techniques involving cermets. Although there are a variety of materials that are capable of producing highly resistive films, these tend to involve very thin films (in the case of metals), reproducibility and uniformity problems (in the case of cermets), or have large TCRs (in the case of semiconductors). We applied a variety of physical vapour deposition techniques for the sputter deposition of films ranging in composition from pure silicon to pure tungsten. In doing so, we have identified a range of compositions and thicknesses in which the TCR and resistivity are independent of thickness, suggesting that these films do not suffer from any significant changes in microstructure at any critical thickness in the range of 70 to 2000 nm. These results were also independent of the type of sputter deposition used. These factors suggest that such films will be useful in the manufacture of stable resistors on the order of 1 kΩ or more.

Electroless copper deposition has been shown to be a viable technique for the fabrication of very large scale integration (VLSI) interconnections. In particular, electroless deposition was found to be able to fill the high aspect ratio features in submicron VLSI technologies. In this work one- and two-dimensional models of electroless Cu deposition are presented. These models are based on the diffusion of the dominant ionic species [Cu(II)] and the surface reaction kinetics. These assumgons result in a nonlinear diffusion equation to be solved. A one-dimensional numerical model is used to determine the diffusivity of the copper ion and the reaction coefficients from experimental results. The two-dimensional model is based on SIMBAD, a thin film growth simulator, which was enhanced by the inclusion of a finite element module to solve the diffusion of the dissolved Cu(II) ion to the film surface. The module automatically generates a triangular grid and has a finite element computational engine capable of solving the diffusion equation with the nonlinear boundary conditions arising in the problem. In order to confirm the predictions of the two-dimensional model, copper films were deposited over high aspect ratio trenches cut into silicon oxide. Simulations using simulation by ballistic deposition (SIMBAD) were found to compare very well with cross-sectional scanning electron micrographs of these films. The numerical models were also used to study the sensitivity of the conformal filling of trenehes and vias to the diffusivity and reaction coefficients. It was found that a 200 seam/void would form in the fi m if the diffusivity was dropped by an order of magnitude.

A continuously twisted, structurally chiral medium (CTSCM) is a reciprocal medium whose constitutive properties vary helicoidally along its axis of spirality (say, the z axis), and the corresponding piezoelectric medium is abbreviatedly called the PCTSCM. Very recent progress in thin-film research is presented here to show that technologically significant CTSCM’s and PCTSCM’s are waiting in the wings and calling for theoretical advances in the understanding of wave excitation and propagation in these novel materials. A spectral Green’s function is obtained as a bilinear composition of two matrices, after implementing a spatial Fourier transform in the xy plane as well as the Oseen transformation. As a result, multilayered media problems as well as grating problems utilizing CTSCM’s and PCTSCM’s become accessible to theoretical exploration leading to novel transducers, sensors, and other devices.

Microfluidic channels (A) were fabricated by a new GLAD method with thin film porosity engineering capabilities. Smooth areas of a substrate result in fairly compact thin film morphology (C) while areas of the same substrate pre-patterned with a periodic array of seeds (B) are quite porous and permit liquid flow.

Branched indium tin oxide (ITO) nanowire networks are promising candidates for transparent conductive oxide applications, such as optoelectronic electrodes, due to their high porosity. However, these branched networks also present new challenges in assessing conductivity. Conventional four-point probe techniques cannot separate the effect of porosity on the long-range conductivity from the intrinsic material conductivity. Here we compare the average nanoscale conductivity within the film measured by terahertz time-domain spectroscopy (THz-TDS) to the film conductivity measured by four-point probe in a branched ITO nanowire network. Both techniques report conductivity increases with deposition flux rate from 0.5 to 3.0 nm s(-1), achieving a maximum of ~ 10 (Ω cm)(-1). Modeling the THz-TDS conductivity data using the Drude-Smith model allows us to distinguish between conductivity increases resulting from morphological changes and those resulting from the intrinsic properties of the ITO. In particular, the intrinsic material conductivity within the nanowires can be extracted, and is found to reach a maximum of ~ 3000 (Ω cm)(-1), comparable to bulk ITO. To determine the mechanism responsible for increasing conductivity with flux rate, we characterize dopant concentration and morphological changes (i.e., to branching behavior, nanowire diameter and nucleation layers). We propose that changes in the electron density, primarily due to changes in O-vacancy concentration at different flux rates, are responsible for the observed conductivity increase. This understanding will assist balancing structural and conductivity requirements in applications of transparent conductive oxide networks.

Iron pyrite is a promising material for photovoltaic power production due to low material extraction and processing costs and high optical absorption. Reliable production of photovoltaic grade iron pyrite thin films has, however, been challenging. One potential fabrication route is the direct conversion of iron-to-iron pyrite by sulfur annealing (sulfurization). Bulk iron thin films are used typically but they can suffer from cracking or delamination. Herein we report the sulfurization of porous, columnar Fe films deposited with Glancing Angle Deposition (GLAD), which allows us to control the inter-column spacing (void-fraction) of the precursor film. We show that the morphology and microstructure of the iron pyrite films are strongly affected by the void-fraction. By precisely tuning the void-fraction of the precursor film at 82 oblique angle incidence deposition we can produce iron pyrite films with increased crystallite sizes >100 nm with a uniform, crack-free, facetted granular microstructure. Large crystallites may reduce carrier recombination at grain boundaries, which is attractive for photovoltaic devices. Further increasing the void-fraction produces a columnar iron pyrite structure. We also report composition, electrical and optical characterization including a 27 ps lifetime of photocarriers measured with ultrafast optical-pump/THz-probe. Structured, porous precursors offer an alternate route to control microstructure and film stress during fabrication of iron pyrite thin films. © 2013 Elsevier B.V.

We explored four different inorganic oxides and determined their merits in miniaturized planar chromatography. Despite progression of chromatographic techniques over several decades, such alternatives to traditional planar silica gel stationary phases have not been fully evaluated. Glancing angle deposition (GLAD) provided an excellent platform for engineering nanostructured thin films in these materials for ultrathin-layer chromatography (UTLC). Separations of carotenoids and synthetic food dyes were used to investigate the attributes of SiO2, Al2O3, TiO2, and ZrO2 GLAD UTLC media. These anisotropic high surface area thin films possessed similar channel-like features but different chromatographic properties. TiO2 and ZrO2 media were especially interesting since analyte retention could be modified through simple oxidation heat treatments and UV irradiation. Generally, oxidation reduced analyte retention while UV exposure increased retention. Changes in retention factor as large as δhRF~40 (for Acid Red 14 on titanium oxide) were achieved. Food dye mixtures were applied using consumer inkjet printers as per the Office Chromatography concept and separation performance was quantified using advanced video instrumentation designed for miniaturized plates. Enhanced time-resolved UTLC methods were used to calculate figures of merit from recorded dye separation videos. Small theoretical plate heights (

We report the fabrication, characterisation, and electro-catalytic activity of

Exploitation of anodically formed self-organized TiO2 nanotube arrays in mass-manufactured, disposable biosensors, rollable electrochromic displays and flexible large-area solar cells would greatly benefit from integration with transparent and flexible polymeric substrates. Such integration requires the vacuum deposition of a thin film of titanium on the desired substrate, which is then anodized in suitable media to generate TiO2 nanotube arrays. However the challenges associated with control of Ti film morphology, nanotube array synthesis conditions, and film adhesion and transparency, have necessitated the use of substrate heating during deposition to temperatures of at least 300 degrees C and as high as 500 degrees C to generate highly ordered open-pore nanotube arrays, thus preventing the use of polymeric substrates. We report on a film growth technique that exploits atomic peening to achieve high quality transparent TiO2 nanotube arrays with lengths up to 5.1 microm at room temperature on polyimide substrates without the need for substrate heating or substrate biasing or a Kauffman ion source. The superior optical quality and uniformity of the nanotube arrays was evidenced by the high specular reflectivity and the smooth pattern of periodic interferometric fringes in the transmission spectra of the nanotube arrays, from which the wavelength-dependent effective refractive index was extracted for the air-TiO2 composite medium. A fluorescent immunoassay biosensor constructed using 5.1 microm-long transparent titania nanotube arrays (TTNAs) grown on Kapton substrates detected human cardiac troponin I at a concentration of 0.1 microg ml(-1).

We demonstrate a novel method to realize ultra-miniaturized on-chip vertical inductors for use in microwave and millimeter-wave devices. The inductor consists of a thin film of closely-packed, vertically aligned nickel nano-posts. The film is fabricated using a glancing angle physical vapor deposition method, which is CMOS compatible. The resulting nanostructured inductors were measured from 10 GHz to 70 GHz and were found to have inductances of 0.1 nH, resulting in 6pH μιη"2, 60 times larger than previously reported planar inductors. A quality factor of 3 is measured and the results indicate that it continues to improve above 70 GHz, while inductance remains constant. Such nanostructured posts could potentially lead to ultra-small, ultra-wideband inductors to preserve space in integrated circuits.