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The generation and characterization of a robust thienylsilane molecular layer on indium tin oxide substrates was investigated. The molecular layer was found to reduce the oxidation potential required for the electrochemical polymerization of 3,4-ethylenedioxythiophene. The resulting electrochemically prepared poly(3,4-ethylenedioxythiophene):poly(p-styrenesulfonate) (ePEDOT:PSS) films were found to be more uniform in coverage with lower roughness and higher conductivity than analogous films fabricated with bare ITO. A relative improvement in the efficiency of 2,5-diyl-poly(3-hexylthiophene) (P3HT)/[6,6]-phenyl-C(61)-butyric acid methyl ester (PCBM) bulk heterojunction solar cells was observed when devices were formed on thienylsilane-modified ITO electrodes, rather than unmodified ITO control electrodes.

High-performance thin-layer chromatography is a separation technique commonly used to identify and quantify components in chemical mixtures. Sophisticated analytical tools are required to extract the full analytical power from this technique and especially for miniaturized planar chromatography its utility has not been harnessed. A new approach uses an elegant, simplified system assembled from ordinary consumer printers and scanners to perform separations on monolithic and nanostructured ultrathin-layer phases. This system is shown to outperform existing planar chromatographic tools for analysis on miniaturized plates. Analysis can be completed in a manner of minutes, running numerous samples in parallel at a reduced cost, with very low sample and reagent volumes, all using a familiar computer interface with common office peripherals.

Glancing angle deposition (GLAD) facilitates the fabrication of nanostructured thin films with varying density, using a motion control algorithm governing substrate movements during film growth, which engineerings the film structure. Film architectures for specific optical applications including photonic crystals are easily produced with GLAD. A challenge in the photonic crystal field has been the realization of in-situ control of optical characteristics. We have demonstrated partial control of stopband optical characteristics using an electric field in a GLAD 1D photonic crystal by the electrophoretic movement of absorbing dye ions.

A three‐dimensional ballistic deposition model for thin film growth has been developed, incorporating the mechanisms of shadowing and relaxation which are essential to microstructure formation. In addition to generating columnar structure similar to that found in films deposited at low temperature, the simulation produces columns which become elliptic cylinders as the angle of incident vapor flux is increased. The model clearly confirms that this structural anisotropy which develops in the film plane is due to self‐shadowing in the growing film. The anisotropy, originally revealed in magnetic and electrical properties of obliquely deposited alloys, appears as the elongation of column structure in a direction perpendicular to the plane of incidence. In agreement with titanium films sputtered using a planar magnetron at 65 mPa argon pressure, simulations show a maximum ratio of column major axis to minor axis of about 2 at a deposition angle of 60°. The effect is seen to decrease in both simulations and rea...

A ballistic deposition model, SIMBAD, has been extended to simulate physical vapor deposition onto substrates at elevated temperatures. The model has been expanded to account for the effect of film curvature on surface diffusion. The effects on via coverage and filling have been simulated for aluminum films, and complete planarization of a 1:1 aspect ratio via is predicted for a temperature of 550 degrees C. Via aspect ratio and sidewall taper can also strongly affect coverage and filling. Biased sputtering has also been incorporated into the model and shows that a primary effect is a substantial reduction in the temperature required to achieve full planarization. However, void formation and substrate damage are problems predicted to occur under some bias sputter conditions. >

A two‐dimensional model for plasma etching has been developed based on simulation by ballistic deposition (SIMBAD), a two‐dimensional model for film growth over topography. By incorporating the effects of shadowing, adatom mobility, and incident flux distributions, SIMBAD is able to predict microstructure and density of films deposited by physical vapor deposition methods such as evaporation and sputtering. The plasma etch has been similarly modeled using an appropriate incident angular distribution for reactive species and a fixed probability of reaction. Simulation predictions are shown to agree well with experimental results for etching of tungsten films sputtered over trenches. For a 0.9‐μm‐thick tungsten film on a 1.8‐μm‐wide 0.6 aspect ratio trench with 80° sidewalls, the etch rate on the sidewalls was found to be about twice the rate on the horizontal sections of film for a CF4/O2 plasma etch. This is in agreement with the computed results.

Obliquely deposited thin films with helical microstructures exhibit circular Bragg effects. In this study, the effect of film porosity on the circular birefringence of helical thin films is investigated in TiO(2) films deposited at angles ranging from 30 degrees to 87 degrees in order to determine the various mechanisms responsible for the circular Bragg effects. Specular transmittance and diffuse scattering measurements indicate two film growth regimes of enhanced circular Bragg effects: The first regime is due to a maximum in form birefringence while the second regime is caused by strong anisotropic scattering.

We present evidence of complete, three-dimensional photonic bandgaps in obliquely deposited thin films with a porous microstructure of tetragonally arranged square spirals. We further present a capability to engineer the bandgap center to wavelengths as low as 1.65 mum, with bandgap widths of up to 10.9%. Using new deposition methods that provide detailed control over the photonic crystal dimensions and morphology, this approach allows advanced photonic crystal architectures to be realized over large scales with uncomplicated fabrication technology.

We present the design, fabrication, and characterization of a GLAD-fabricated photonic crystal sensor with a bandgap located in the visible optical spectrum. The photonic crystal is fabricated from TiO2 using electron-beam evaporation in a GLAD capable vacuum deposition system. Changes in humidity over a wide range (from 3% to 90% relative humidity) are detected by a colour change in the film due to movement of the photonic bandgap. The colour changes are quantified by measuring the transmittance of white light. Coupling the sensitivity of the film with a simple visual feedback system eliminates the need for complicated measurement techniques. This is desirable to minimize the cost and power consumption of the sensor device, making it amenable to large-scale production and deployment.

We have demonstrated the use of tetrahydrofuran (THF) annealed self-assembled monolayers of polystyrene-b -poly(2-vinylpyridine) diblock copolymer to produce hexagonal close packed metallic nanoarrays which may be used as substrates to produce ordered nanostructured optical thin films using glancing-angle deposition. Our film connects the sites of a face-centered cubic lattice using a triangular spiral deposited on the block copolymer seeds. The optical properties of unseeded and seeded triangular spiral thin films are characterized. While the nanostructured thin films can inherit the periodicity of the underlying seeds, the optical performance is less than that of an unseeded film. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

ZnO thin films were fabricated using PLD, sputtering, e-beam evaporation and sol-gel techniques. The films were annealed in an oxygen environment to improve their crystallinity. Photoluminescence efficiency and angular emission patterns were characterized and are reported in absolute radiometric units. Conversion efficiencies in the range of 1 – 7 · 10-6 were found for the PLD films, 7 · 10-6 for a sputtered film, 7 – 40 · 10-6 for the e-beam evaporated films, and 20 – 400 · 10-6 for the Sol-Gel films. In most cases, the angular emission pattern of the photoluminescence was lambertian in nature. Non-lambertian emission patterns were observed for some films with microstructure, achieved with PLD and e-beam evaporation. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

A dry etch recipe was developed for porous nanostructured TiO2 thin films fabricated using glancing angle deposition (GLAD). Unlike wet chemical etches, the technique reported here preserves the vertical post nanostructure, eliminating clumping. A highly controllable and easily tailored reactive ion etching process with CF4 alone, or combined with O2, was investigated. The anisotropic etch modifies the morphology and density of standard GLAD films, which is of interest for sensing applications.

A new interferometer-based optical sensing platform with nanostructured thin films of ZrO2 or TiO2 as sensing environment has been developed. With the application of an IC compatible Si(3)N(4) waveguide technology, Mach-Zehnder interferometer devices have been fabricated. The application of the glancing angle deposition technique allowed fabrication of nanostructured thin films as the optical sensing environment. Sensing ability of fabricated devices has been demonstrated through the refractive index measurement of a known gas. The transmission spectra and time response measurements have demonstrated a maximum phase shift of Delta phi=pi/10 and a |Delta P(out)|=0.65 dBm. Devices with TiO2 film on the sensing region performed much better than devices with ZrO2, with sensitivity twice as high.

We report measurements of bolometric absorption and absolute reflectivity of a thin film of NbN on a silicon substrate, above and below the superconducting transition temperature of 13.3 K. The opening of the gap at an energy of 3.9 kB Tc is seen clearly in both types of measurement. The data are compared with the predictions of the Mattis-Bardeen theory. The change in the reflectivity and the absorption at energies above 2.6. is larger than that calculated from the theory. By an analysis of the reflectivity data, it is shown that the theoretical values of the complex superconducting conductivity are too high. Thin films of superconducting NbN are of great current interest because of their very low surface resis­ tance, which is comparable to that of Nb, and relatively high values of Tc (13-18 K). This is important for mi­ crowave device applications. Films made from the re­ cently discovered high-Tc ceramic materials have so far exhibited higher surface resistances. A recent study by Oates et al. 1 reported measurements of the temperature and frequency dependencies of the surface impedance of NbN thin films in the microwave region using a stripline resonator and cavity technique. They satisfactorily fitted the temperature dependence of the 35 GHz surface resis­ tance by use of the weak-coupling dirty-limit Mattis­ Bardeen theory,2 but they also noted that their sensitivity was insufficient to differentiate between weak and strong coupling. In the far-infrared region, which contains the energy gap, measurements of transmission through thin NbN films have been reported by Karecki, Pena, and Per­ kowitz. 3 They found it impossible, however, to satisfac­ torily fit the data with a dirty-limit assumption in which the scattering time 7=0 and the normal conductivity has no frequency dependence. Instead they used their fit to obtain a value of 7. One of the important potential appli­ cations of NbN is in tunnel junctions, and measure­ ments4.5 using these devices have also shown the energy­ gap and phonon density of states. We have recently6 used a bolometric method in which the absorption A is measured directly in an attempt to measure the energy gap in the 10 K organic superconduc­ tor, (BEDT-TTF)2Cu(NCS)2' where BEDT-TTF is bis(ethylenedithio) tetrathiafulvalene. These measure­ ments showed no sign of a superconducting gap, so it was important to test our methods with a better understood conductor. Using the NbN samples, we have successfully observed the energy gap as a function of temperature in thin-film NbN with high resolution and good signal to noise. We then measured the power reflectivity and again saw the gap clearly. We found a large discrepancy with

Density and resistivity of sputtered tungsten films are directly measured as a function of angle‐of‐vapor incidence. The film density is found to drop off quickly at deposition angles greater than 50°, and the resistivity rises sharply at angles greater than 70°. These deposition angle effects in films deposited over topography can be predicted using simulation by ballistic deposition (SIMBAD), a two‐dimensional computer simulation of thin‐film growth using ballistic deposition of hard disks. Simulated film structure and density is in good agreement with real tungsten films deposited over vias. To confirm density predictions, etch rate measurements made on planar films are presented which confirm the dependence of etch rate on film density. The results of the measurement are used to develop an etching algorithm using SIMBAD density predictions. Films deposited over vias are etched to reveal the presence of low‐density regions of film covering the via sidewalls, showing excellent agreement with the simulat...

A simulation by ballistic deposition model (SIMBAD) has been developed to predict thin‐film microstructures of films deposited over topography. In order to study the radio frequency (rf) bias planarization process, this model has been extended to include film resputtering, redeposition, ion reflection, and ion‐induced diffusion. To test the resulting SIMBAD simulations, tungsten was bias sputter deposited over high aspect ratio grooves. The resulting films exhibited increased sidewall coverage and planarity. Ion milling effects were also observed. These features were qualitatively matched by SIMBAD predictions as were microstructural details, such as column orientations and void locations. This preliminary success shows that such SIMBAD simulations can be useful in understanding and optimizing the rf bias planarization process.

Controlled-porosity Si thin films suitable for use as high-aspect-ratio microbattery electrodes were produced using the glancing angle deposition (GLAD) technique. GLAD is a high-vacuum physical vapor deposition method that can be used to produce a variety of film morphologies from most vacuum-compatible materials. No lithographic steps were required to create the porous, columnar thin films. Initial electrochemical results indicate large gravimetric and areal capacities (3600mAh∕g, 90μAh/cm2, respectively), and good capacity retention (3000mAh∕g after 70 charge/discharge cycles) can be obtained from Si vertical post morphology films. Areal capacity and capacity retention can likely be further improved by optimizing the film morphology, electrode material composition, and cycling conditions.

The use of self-assembled block copolymer structures to direct the formation of large area nanoscale features could provide a silicon-based fabrication-compatible means to supplement conventional lithographic techniques. Here, self-assembled monolayers of polystyrene- b -poly(2-vinylpyridine) (PS- b -P2VP) diblock copolymer were utilized as structural elements for the production of pseudo-hexagonal close packed metallic nanoarrays. Metal ion loading of the P2VP block with simple aqueous solutions of anionic metal complexes is accomplished via protonation of this basic block, rendering it cationic; electrostatic attraction leads to a high local concentration of metal complexes within the protonated P2VP domain. The ordering of the copolymer micelles can be enhanced by solvent vapor annealing. The resulting templated large area metallic nanoclusters can serve as periodic seeds to grow nanofibrous thin films, which inherit the periodicity of the underlying seeds, by glancing angle deposition (GLAD). GLAD offers a high level of control over the composition and porosity of thin films microstructures, and has been used to make uniform and highly porous thin film architectures for applications such as photonic crystals.

Periodic high-/low-index film stacks composed of Y(2)O(3) : Eu were grown by glancing angle deposition on silicon and fused silica substrates. Postdeposition annealing at temperatures from 600 to 1000 degrees C for 1 h in air was performed to activate photoluminescence. Absolute photoluminescence spectra were obtained as a function of observation angle. The angular emission distribution was non-Lambertian, with peak emission at angles of 50 to 60 degrees with respect to substrate normal. Spectroscopic transmittance and ellipsometry measurements were performed to characterize the films. Using this description, we were able to reproduce the angular photoluminescence patterns of the films.

Luminescent thin films are used for many applications, including light-emitting diodes, lasers and flat panel displays. Glancing angle deposition (GLAD) is a physical vapor deposition technique which relies on highly oblique flux angles to create porous thin films. When combined with real-time substrate motion control and measurement of deposition rates, it is possible to produce high quality nanostructered thin films. A rugate filter uses a sinusoidally varying index profile to produce a stop band. Using the GLAD technique, it is possible to produce a rugate filter from a single material. The central wavelength, depth and width of the stop band can be designed by adjusting the film nanostructure. In this paper, rugates composed of Y 2 O 3 :Eu are used to control the angular emission profiles of the photoluminescent thin film. Confined, annular and isotropic emission profiles film is nearly uniform for emission angles between ~ -60° and ~60°.

Glancing angle deposition (GLAD) is a physical vapor deposition technique that depends on a highly oblique flux angle to create porous, large surface area thin films via self-shadowing. Control of the deposition parameters may provide a means to tune film porosity for zinc oxide sensors and photovoltaic devices. However, the self-shadowing mechanism requires a collimated particle flux, and therefore GLAD performs best under high vacuum. Creating structured films with sputtered GLAD is difficult since the high chamber pressure (>1 mTorr) necessary to maintain the sputter plasma reduces the mean-free-path of flux particles to less than 100 mm. By using an aperture to reduce the angle subtended by the target from the perspective of the substrate, maintaining an argon plasma pressure of 1.4 mTorr, and reducing the throw distance to less than 50 mm we were able to produce structured, polycrystalline, zinc thin films via GLAD. At oblique flux angles, highly porous films consisting of randomly oriented nanorods are grown. The nanorods have diameters between 10-100 nanometers with lengths up to several micrometers. Annealing at temperatures up to 250 °C in air produces polycrystalline zinc oxide with minimal changes to the film structure. We present details of the thin film fabrication process for the convoluted nanorod film morphology. We report characterization results for films produced at several deposition angles before and after annealing using scanning electron microscopy (SEM), X-ray diffraction (XRD), and transmission electron microscopy (TEM).

Reactively sputtered InN films were prepared with a band gap of 1.70±0.02 eV, carrier concentrations of 2×10 20 cm −3 and mobilities of 9 cm 2 V −1 s −1 . Optical constants were determined from analysis of the transmission and reflection spectra in the spectral region 0.7–2.7 microm. These constants showed a behaviour consistent with the effects of free carrier absorption. The Drude free electron theory was used to calculate the high frequency lattice dielectric constant, found to be e ∞ =6.6. The imaginary part of the dielectric constant e 2 , followed a proportionality e 2 ≈ λ 2.7 in the wavelength region above the band edge and below the plasma wavelength of 2.8 μm. This behaviour is typical of the scattering of electrons by ionized impurities such as nitrogen vacancies.

MgF2 films were evaporated at angles of incidence of 5° and 40° onto oxide lines 1.5 μm wide on a silicon wafer. The film properties observed by scanning electron microscopy studies of cleaved cross-sections were compared with those predicted by simulation by a ballistic deposition model. Good agreement was found for the surface profiles of the films, the orientation of the columnar microstructure and the location of porous low density regions.

The variation of the properties of niobium nitride (NbN) thin films as a function of argon partial pressure and nitrogen flow were studied. The films were deposited by dc reactive planar magnetron sputtering onto unheated substrates. All of the films were superconducting and had the B1, face‐centered cubic crystal structure. A number of films deposited at argon partial pressures of 5 and 7 mTorr had superconducting critical temperatures (Tc ) of 15.6 K and grain sizes of 100–120 nm. The film morphology showed a zone 1 to zone T transition as the argon partial pressure was decreased from 12 to 5 mTorr. Films deposited below 5 mTorr exhibited excessive tensile stress (>1.9×109 N/m2) and delaminated from the substrate.

A density profile for sputtered metal deposited over a step is generated using simulation by ballistic deposition (simbad), a two‐dimensional computer simulation of thin film growth by ballistic deposition of hard disks. By postdeposition etching of a real Mo film deposited over a similar step, regions with high etch rate are identified. As etch rate is related to density, these are assumed to be low density sections, and are in fact found to agree well with low density regions predicted by the simulations.

The two-dimensional simulation by ballistic deposition of sputtered metal deposited over a 1.5- mu m step and a large variety of vias and contacts is presented. The sizes of the vias and contacts are varied from 1 to 3 mu m, and three different sidewall topographies are simulated. In addition, simulated film growth over a stacked via/contact is presented. The step coverage of each film is determined, and surface profiles are provided at different growth intervals. The use of SIMBAD, a ballistic deposition technique, provides information unattainable through the use of conventional film deposition simulations. In addition to the step coverage available from conventional simulations, density profiles of the simulated films are produced and the columnar microstructure is analyzed. Finally, conclusions are inferred as to the quality of real films deposited over each via geometry. >

We have used the glancing angle deposition technique to fabricate highly porous nanostructured optical thin films that act as humidity sensors. The responsiveness and repeatability of these sensors has been investigated for samples stored under different environmental conditions. It has been found that samples stored in air have a more stable performance than those stored in a dry nitrogen environment. It has also been found that annealing impacts the responsiveness of the optical thin film sensors.

Glancing angle deposition (GLAD) is a thin film fabrication method providing dynamic control over the internal columnar microstructure of the deposited film. Using the GLAD technique it is possible to control the porosity of the coating allowing precise tailoring of the optical properties. Therefore, in a single material system, the refractive index profile of the film can be engineered to create a variety of multilayer structures. The focus of this research is on the optical properties of these structured thin films. When the structure is periodic, incident radiation is subject to constructive and destructive scattering which lead to photonic bandgap effects. Also of interest are the optical properties of aperiodic systems, such as the Thue-Morse multilayer, which are deterministic but non-periodic. The complex structural correlations in aperiodic systems lead to interesting bandgap-like properties. Applying the GLAD technique, periodic and aperiodic optical lattices are fabricated with titanium dioxide, a dielectric material commonly used in optical coating devices. The bandgap properties of these systems are investigated using transmittance spectroscopy and transfer matrix calculations.

Chiral optical filters are characterized by circular Bragg effects, including the preferential reflection and transmission of circular polarization states. The selective response to circularly polarized light is caused by stratified birefringent plates twisted into a helical arrangement, as seen in cholesteric liquid crystals and columnar thin films produced by oblique-angle physical vapor deposition. A refinement of the latter, glancing angle deposition employs substrate rotation to control the optical anisotropy of columnar thin films, and was used in this study to suppress the reflection sidelobes of chiral optical filters by modulating the local birefringence of helically structured thin films using an apodization function. Both theoretical simulations based on Berreman formalism, and experimental results involving evaporated TiO(2) thin films are presented and compared.

Ultrathin layer chromatography (UTLC) is a relatively new variant of thin layer chromatography, with a 10 μ m thick monolithic silica sorbent layer that gives faster separations with lower limits of detection and reduced analyte and solvent volumes. We have produced UTLC plates with controllable nanostructure and thickness, and show that the layer separation characteristics depends on the film nanostructure. We also show that layers made with in-plane anisotropic nanostructures will exhibit a decoupling effect, where the analyte spots do not develop in the same direction as the solvent front movement. The added layer morphology and material selection adds a degree of freedom to UTLC, and may have applications in multi-dimensional TLC.

We present a novel method of modulating total internal reflection (TIR) from an optical surface using a solution of dye ions in combination with a nanostructured electrode. Previous work using the electrophoretic movement of pigment particles to modulate TIR was limited by agglomeration of the pigment over time. Dye ions do not suffer from this limitation, but because of their small size they have significantly smaller absorption cross-section per unit charge than pigment particles which are generally two orders of magnitude larger. This significantly limits the maximum absorption caused by electrostatic attraction of the ions to a transparent conductive electrode. This can be overcome by using a transparent conductive nanoporous thin film as the electrode in which the porosity increases the effective surface area, allowing more dye ions to move into the evanescent wave region near the nanoporous transparent electrode and thus substantially increases the amount of absorption. In this paper, we demonstrate the modulation of TIR by observing the time-dependent variation of the reflectance as the dye ions are moved into and out of the evanescent wave region. This approach may have applications in reflective displays and active diffractive devices.

Titanium dioxide thin films were formed by electron-beam evaporation onto fused silica substrates using serial bideposition (SBD). The SBD technique combines rapid substrate rotation and oblique-angle physical vapor deposition (PVD) to create optical coatings that are composed of nanostructured columns which exhibit large birefringence values in the plane of the substrate. In this study, post-deposition annealing was used to crystallize amorphous TiO 2 thin films formed by SBD to improve birefringence without significantly increasing optical absorption or scattering. Birefringent thin films were fabricated at deposition angles ranging from 60° to 75° and annealed in air at temperatures ranging from 200°C to 900°C to form anatase and rutile TiO 2 . Changes in the optical properties, crystallinity, and nanostructure were characterized by ellipsometry, x-ray diffraction, atomic force microscopy, and scanning electron microscopy. It was found that optical anisotropy increases strongly upon formation of anatase, yielding in-plane birefringence values that doubled from 0.11 to 0.22 in the case of TiO 2 thin films deposited at 60° and annealed at 400°C. Raising the annealing temperature to 900°C to form rutile thin films increased the thin film birefringence further but also led to low optical transparency due to increased absorption and diffuse scattering.

Transparent electrically-conductive nanoporous thin films can be used as electrodes to attract dye ions from solution to modulate the reflectance of a surface. Here we demonstrate that this technique can be used to create diffraction gratings that can be modified by the application of a small electrical potential with a selected spatial distribution. Using nanoporous ITO films fabricated by Glancing Angle Deposition, we have produced variable diffraction gratings, fabricated by a variety of methods, including lithography combined with etching techniques or direct patterning using focused ion beam etching. We demonstrate modulation of the diffraction pattern by employing electric force to attract the dye ions into the nanoporous electrode, thereby introducing a substantial local change in the effective refractive index value and thus altering the resultant diffraction pattern and, in some cases, yielding diffractive orders that lie between those associated with the underlying grating. These new orders are easily distinguished and their intensity can be substantially modified by controlling the applied voltage. Because this technique can work with very small pitch gratings, this approach has the potential to enable new applications that may not be readily achieved using conventional liquid crystal technology.

The effects of substrate surface energy and vapor deposition rate on the initial growth of porous columnar tris(8-hydroxyquinoline)aluminum (Alq3) nanostructures were investigated. Alq3 nanostructures thermally evaporated onto as-supplied Si substrates bearing an oxide were observed to form a solid wetting layer, likely caused by an interfacial energy mismatch between the substrate and Alq3. Wetting layer thickness control is important for potential optoelectronic applications. A dramatic decrease in wetting layer thickness was achieved by depositing Alq3 onto alkyltrichlorosilane-derivatized Si/oxide substrates. Similar effects were noted with increasing deposition rates. These two effects enable tailoring of the wetting layer thickness.

Photonic crystals currently hold exciting potential in waveguiding applications with the ability to greatly reduce waveguide bend radii, allowing for the realization of photonic networks with increased complexity and device density. Square spiral photonic crystals are comprised of periodic arrays of slanted cylindrical columns with periodic abrupt 90° changes in the column growth direction. The abrupt changes produce elbows which correspond to points in the three-dimensional diamond lattice, which are commonly referred to as diamond:n photonic crystal structures based on the nth nearest neighbor lattice point between column arms. The diamond:n structures are characterized by four parameters: column separation, spiral pitch, column diameter, and column growth angle. These structures have been shown theoretically to have a three-dimensional relative bandgap of approximately 15% for a direct silicon diamond:1 structure and approximately 24% for an inverse silicon diamond:5 structure with circular column cross sections. Silicon square spiral photonic crystals can be grown by a single-step thin film deposition process known as glancing angle deposition (GLAD), which utilizes rotation of lithographically patterned substrates and advanced control algorithms. While using GLAD to grow square spiral photonic crystals in a single-step process is desirable, it does have inherent limitations. Physical vapor deposited films deposited at oblique incidence angles form columns with angle ≤ 60° relative to the substrate normal. This deviates from the optimal diamond:1 and diamond:5 structures which require film growth angles of approximately 64° and 74°, respectively. Here we present SEM images of periodic silicon square spiral films grown with a vapor source incidence angle of 85° that indicate an average column tilt angle of 57˚ for films grown with the basic GLAD process and an average column tilt angle between 61˚ and 65˚ using an ion-assisted GLAD process. Photonic simulations indicating that square spiral films with complete three-dimensional photonic bandgaps are only achievable via ion-assisted GLAD are also presented.

The electrical resistivities of nanostructured films of indium tin oxide were measured. The films were prepared using glancing angle deposition, a physical vapour deposition technique. This technique was used to prepare nanostructured indium tin oxide thin films of various morphologies. Films consisting of vertical posts were electrically characterized using a probing station. Compared to a normally evaporated planar film, the nanostructured films were found to exhibit resistivities approximately two orders of magnitude greater. Development of the measurement technique is ongoing, and several ideas for improvement are described.

We re-examine the potential drop method to give a direct estimation of the absolute error in transmission-line matrix (TLM) diffusion modelling. In particular, the open-circuit boundary is taken into account. Promising results are presented with a structure relevant to thermal analysis of semiconductor devices. © 1998 John Wiley & Sons, Ltd.

In toxicology and industrial hygiene, fibrous aerosols have long been associated with health risks. Aerodynamic alignment with inhaled air streamlines allows long, cylindrical fibers to penetrate deep into the lung, whereas compact particles of similar mass are filtered out in the upper respiratory tract. For drug delivery applications, fibrous aerosols may thus enable a relatively large drug mass to be delivered to the distal regions of the lung. At present, the aerodynamic behaviors of fibers that influence deposition in the respiratory tract are discussed. Methods for generating monodisperse (in both diameter and length) fibrous aerosols and of tagging these aerosols with a UV absorbent material, both by physical vapor deposition, are outlined.

Presented here are the results of a study on the effects of varying the porosity of unique nanostructured thin films on their humidity sensing properties. 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. Also presented are the results of surface functionalization effects on device sensitivity. It was found that the dynamic range of the sensors could be attenuated by as much as three orders of magnitude by covalently bonding hydrophobic organic molecules to the surface of the films.

Chemical treatments, when applied to nanostructured oxide thin films, can be used to generate added functionality in many devices. In this study, a nanostructured defect-mode optical filter was prepared by glancing angle deposition of titanium dioxide and functionalized with 3,3,3-trifluoropropyl-trichlorosilane to render the thin film insensitive to variable humidity conditions. Electrical characterization and contact angle measurements demonstrate that the hydrophilic thin film becomes hydrophobic when functionalized, and transmission measurements clearly show that the wavelength shift of the defect-mode becomes strongly inhibited for a wide range of humidity levels., Series: MRS Online Proceedings Library

Periodic high-/low-index film stacks of Y2O3:Eu were grown with varying periodicities us-ing the glancing angle deposition (GLAD) technique onto silicon and fused silica substrates. Post-deposition annealing at temperatures from 600 to 1000°C for 1 hour in atmosphere was per-formed to enhance the photoluminescent output of the films. The films were optically character-ized using transmission measurements and Mueller matrix ellipsometry. The luminescence was measured using a spectrometer calibrated for absolute intensity measurements using a frequency-quadrupled Nd:YAG pulsed laser as an excitation source. Absolute conversion efficiencies were measured for the films by characterizing the angular emission profile. The angular emission pro-file of the films was found to follow a non-Lambertian emission profile, with peak emission in-tensities at 50° to 60° with respect to the substrate normal., Series: MRS Online Proceedings Library

The fabrication of one dimensional photonic bandgap nanostructures is described and the optical properties of these structures are examined. Using a deposition technique known as a glancing angle deposition (GLAD), porous films with a predefined nanoscale geometry are created. Specifically, in the present work we consider GLAD fabricated thin films characterized by periodically varying refractive index in one-dimension. We introduce a variety of planar defect layers into the structures and investigate the resulting changes observed in the photonic bandgap of the system. Theoretical simulation of transmittance spectra of GLAD fabricated films is performed with the finite-difference time-domain (FDTD) method and the results are compared with experimental measurements. Modifications of the transmittance spectra are investigated by changing the geometry of the defect layer and varying the void region effective index. It is shown that the spectral width and location of states within the bandgap is controlled by the geometry of defect and film microstructure. Active tunability of the defect states is obtained by considering infilling of the void regions of the structure with nematic liquid crystals and then analyzing the optical spectrum for various orientations of the liquid crystal director axis., Series: Proceedings of SPIE

Glancing angle deposition is used to create porous liquid crystal alignment layers with high aspect-ratio, three-dimensional features. We use solid-state deuterium nuclear magnetic resonance to determine the alignment of alpha deuterated 4′ -pentyl-4-cyanobiphenyl in a 3.2 μm thick Si O2 film comprised of independent, helical structures. Comparing measured spectra with models, we determine that the liquid crystalline molecules exhibit chiral ordering dictated by the features of the template films. In the plane of deposition the liquid crystalline molecules tilt away from the substrate normal at an average angle of 51°, which is commensurate with the helical features of the chiral template.

An optical-based humidity sensor with a sub-second response time was fabricated from a nanostructured titanium dioxide thin film. A refractive index profile designed to yield a narrow-bandpass optical interference filter was obtained through nanoscale porosity variations produced by glancing angle deposition (GLAD). Under varying humidity conditions the transmittance spectrum of the filter shifts due to effective index changes of the porous structure resulting from adsorption/desorption of water vapor. In the following we will show 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., Series: MRS Online Proceedings Library

Photoluminescent nanostructured thin films have been fabricated using physical vapour deposition and the glancing angle deposition (GLAD) technique. Precision controlled substrate motion and oblique incidence (>75 o ) enable the fabrication of a variety of 3-D morphologies including vertical posts, helical (chiral) columns and chevrons. Scanning electron microscopy and X-ray diffraction were used to characterize the film nanostructure. These experiments focussed on the chiral morphology which exhibits intriguing polarization behaviour such as selective transmission of circularly polarized light and circularly polarized photoluminescence. Helical films of Y 2 O 3 :Eu and Alq 3 were fabricated with thicknesses in excess of 2 μm and densities nominally 60% of bulk. Transmission spectroscopic ellipsometry measurements were used to determine the degree of selective transmission of polarized light through the samples. The degree of circular polarization for the photoluminescent light emitted from helical films was measured with the use of a quarter waveplate and linear polarizer. Polarized photoluminescence efficiencies were consistent with the observed selective transmission of circularly polarized light through the films. The use of GLAD to control the nanoscale morphology of the films allows for the spectral location and strength of these polarization effects to be easily and accurately selected.