This PDF file contains the front matter associated with SPIE Proceedings Volume 7041, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and the Conference Committee listing.

Frequency modulation (FM) and amplitude modulation (AM) atomic force microscopy have been used to image self-organised assemblies of octanethiol-passivated Au nanoparticles adsorbed on SiO₂/Si(111) samples (where the oxide is either 200 nm or ~ 2 nm thick). Imaging at negative frequency shifts - i.e. in the attractive force regime - in FM mode in ultrahigh vacuum we measure nanoparticle heights which are over 50 % larger than those measured using conventional ("repulsive mode") tapping mode imaging in air. A similar difference in nanoparticle height is observed for attractive mode imaging in air. For nanoparticles adsorbed on 200 nm thick oxide layers, force-distance (F(z)) spectra (measured in FM mode) comprise both a van der Waals component with the conventional power law (1/z²) dependence and a strong electrostatic force which is best fitted using a logarithmic function of the form ln(1/z).

Semiconductor epitaxial self-assembled quantum dots (SAQDs) have potential for electronic and optoelectronic applications such as high density logic, quantum computing architectures, laser diodes, and other optoelectronic devices. SAQDs form during heteroepitaxy of lattice-mismatched films where surface diffusion is driven by an interplay of strain energy and surface energy. Common systems are Ge_xSi_1-x/Si and In_xGa_1-xAs/GaAs. SAQDs are typically grown on a (001) crystal surface. Self-assembled nanostructures form due to both random and deterministic effects. As a consequence, order and controllability of SAQD formation is a technological challenge. Theoretical and numerical models of SAQD formation can contribute both fundamental understanding and become quantitative design tools for improved SAQD fabrication if they can accurately capture the competition between deterministic and random effects. In this research, a stochastic model of SAQD formation is presented. This model adapts previous surface diffusion models to include thermal fluctuations in surface diffusion, randomness in material deposition and the effects of anisotropic elasticity, anisotropic surface energy and anisotropic diffusion, all of which are needed to model average SAQD morphology and order. This model is applied to Ge/Si SAQDs which are group IV semiconductor dots and InAs/GaAs SAQDs which are III-V semiconductor dots.

Microstructure of a nanostructured film is not only of fundamental scientific interest but also an important subject from the practical point of view. In this paper we will discuss the formation of biaxially textured film under extreme shadowing during growth. Biaxially textured films are not single crystals, but they possess both the out-of-plane and in-plane preferred orientations. We will also discuss our newly developed reflection high-energy electron diffraction (RHEED) surface pole figure technique and how we employ this technique to capture the evolution of growth front texture.

Reinforced films based on sulfonated polystyrene cross-linked with water-soluble sulfonated carbon nanotubes were fabricated using a free-standing film-making method. Transmission and scanning electron microscopy, X-ray photoelectron spectroscopy, and thermo-gravimetric analysis were used to verify the cross-linking reaction. The mechanical properties of these films demonstrated that the tensile strength increases with an increase in the sulfonated nanotube concentration. At 5 wt% nanotube loading, the tensile strength increased 84% compared with polymer containing no nanotube loading. The relationships between structure and mechanical properties are discussed and a possible direction for making ultra thin and ultra lightweight film is proposed

The microstructure and optical properties of alumina and titania multilayer coatings prepared using atomic layer deposition (ALD) has been investigated. The titania layers were prepared using TiCl₄+H₂O as the precursors while two different precursors, Al(CH₃)₃+H₂O and AlCl₃+H₂O, were used to deposit the alumina layers. The results show that ALD can be used to produce amorphous, stoichiometric alumina and titania thin films with uniform thicknesses at low temperatures (120 °C). An antireflective coating design based on 4 alternating layers of titania and alumina was prepared and the resulting reflectance compared to theoretical calculations. The results demonstrate that ALD is a suitable technique for the deposition of optical thin films at temperatures compatible with thermally sensitive substrates.

Surface plasmon resonance (SPR) and guided wave SPR (GWSPR) are widely used in sensing. Efforts to improve the sensitivity and stability of these sensors are done by using different multilayer nanostructures such as with the long range SPR and the use of combinations of materials such as gold and silver. Silver based SPR sensors have high sensitivity but a poor stability because of the interactions with water and air. We have shown both theoretically and experimentally that by using the silver based SPR sensor with a 10-15 nm top layer of dielectric film with a high value of the real part ε' of the dielectric function, it is possible to improve the sensitivity of the sensor by few times. The imaginary part ε'' of the top nano layer's permittivity needs to be small enough in order to reduce the losses and get sharper dips. The stability of the sensor is also improved because the nano layer is protecting the silver from interacting with the environment. The calculated evanescent field is enhanced near the top layer - analyte interface, thus the enhancement is due to this and due to an increase of the interaction length as a waveguiding effect.

The optical properties of the sandwich structures of Ag nanorod array (NRA)/dielectric layer/Ag mirror have been investigated theoretically and experimentally. Calculations based on a simple model by treating the NRAs as uniform effective media indicate that the antireflection condition is realized by changing the thickness of the dielectric layer and that the Ag nanorods absorb most of the incident light. The designed structures have been successfully fabricated by taking advantages of the dynamic oblique-angle deposition technique. Under the experimental antireflection condition, Raman scattering measured on the Ag NRA in the near infrared region exhibits significant enhancement. This indicates that the local electric field close to the Ag nanorods can be controlled by the interference of light in the nanostrutured sandwiches.

When a sculptured thin film (STF), made of a metal and ≤ 50 nm thick, is used in lieu of a dense layer of metal in the Kretschmann configuration, experimental data for a STF comprising parallel tilted nanowires shows that a surface plasmon resonance (SPR) can still be excited. As the porosity of the chosen STF increases, experimental data and numerical simulations indicate the SPR dip with respect to the angle of incidence of the exciting plane wave widens and eventually disappears, leaving behind a a vestigial peak near the onset to the total-internal-reflection regime.

Photonic crystals of finite thickness based on porous silicon were designed aiming at their subsequent use in the field of optical chemical- and bio-sensing. These structures consist in nanometric porous silicon rods arranged as to form a triangular lattice embedded into a silicon slab, resulting in dielectric structures that have two-dimensional periodicity and the use of index guiding to confine light in the third dimension. These structures enable the fabrication of photonic crystals in thin dielectric slab systems. The photonic band structure for the odd and even modes was calculated as a function of the thickness of the slab, finding a significant dependence on this parameter. The existence of a photonic band gap for even modes was verified and its size was maximized. In addition, the component of electric and magnetic field distribution perpendicular to the two-dimensional plane for the lowest-order even guided mode was analyzed.

Electromagnetic surface waves are known to propagate along metal-dielectric interfaces (surface plasmon-polaritons) as well as along dielectric-dielectric interfaces (Dyakonov waves) if the two dielectrics have different spatial symmetries. Columnar and sculptured thin films, which are optically biaxial nanomaterials, may be grown on either metallic or dielectric substrates. Both surface plasmon-polaritons and Dyakonov waves can exist at the interface of a thin film and an appropriate substrate. The direction of propagation relative to the thin-film morphology is, in general, limited, and depends on the material and the vapor deposition angle used during fabrication. At the interface of a chiral sculptured thin film and an isotropic dielectric substrate, surface-wave propagation occurs over a much wider angular range and may allow for the first experimental observation of a Dyakonov wave. The characteristic properties of the surface wave, such as phase speed and decay rate, are dependant on the direction of propagation and the vapor deposition angle. As engineered nanomaterials, thin films offer a controllable medium for surface-wave propagation which may be tailored to exhibit specific characteristics. The porosity of the thin films may also offer certain technological advantages.

A sculptured nematic thin film (SNTF) is an assembly of parallel nanowires that bend in a fixed plane orthogonal to the substrate on which the film is deposited. The absorbances, reflectances, and transmittances of linearly polarized, obliquely incident light were calculated for a planar SNTF-metal interface in the Kretschmann configuration. Empirical data on aluminum for the metal and titanium-oxide SNTFs were used for the calculations. The solution of the boundary-value problem for the Kretschmann configuration revealed that more than one surface-plasmon-polariton (SPP) waves can be excited at the planar interface of a thin metal film and an SNTF.

When an electromagnetic wave interacts with a nano structured metallic surface or a nanoparticle, the electromagnetic fields near the surface are greatly enhanced by factors up to 1000. This phenomenon is due to two processes: (i) the 'lightning rod' effect, conventionally described as the crowding of the electric field lines at a sharp metallic tip and (ii) the excitation of localized surface plasmons at the metal surface. Both are responsible for the enhancement of fluorescence, second-harmonic generation and Raman scattering. For metal nanoparticles often both processes are involved in creating the localized enhanced near field. Since sculptured thin films (STFs) can have a rod like structure and an overall large porosity, it is expected that these structures will exhibit enhanced fluorescence and Raman signals. Results of comparative study of surface enhanced fluorescence are presented from STFs containing metal nano structures. The highest enhancement is found for Ag based STFs giving an enhancement factor of x14.

We have demonstrated high-temperature glancing angle deposition (HT-GLAD) of Al on a heated substrate with trench patterns. The nanowhiskers grow not only on the illuminated sidewall but also on the shadowed sidewalls, while few nanowhiskers grow on the shadowed region at the bottom of the trenches. In addition, the size and number of nanowhiskers growing on the sidewall depend strongly on the angle between the incident direction of the vapor flux and the trench directions, although actual angle of inicidence of the vapor flux on the sidewall is kept constant. In order to understand the peculiar growth of Al nanowhiskers, novel transport processes of Al atoms other than surface diffusion need to be elucidated. The reflective scattering on the sidewalls of the trenches is likely to play an important role in the growth of nanowhiskers. On the other hand, we demonstrate the HT-GLAD of metals other than Al. It has been found that nanowhiskers of Cu, Ag, Au, Mn, Fe, Co, Ni and Zn as well as Al grow on the substrates of SiO₂. The robustness in the selection of materials suggests that HT-GLAD is a general method for growing metal nanowhiskers. However, since growth mode of nanowhisker is complicated, further detailed investigation is required for fully understanding of the growth mechanisms of the nanowhiskers by HT-GLAD.

The response to applied electric fields of vanadium dioxide thin films above and below the phase transition is shown experimentally to depend on the size of grains if below ~200nm across, and on aluminum doping above a critical concentration. T_c drops as doping level increases, but does not depend on grain size. The observed phase transition undergoes a remarkable qualitative shift as the applied field goes from optical to low frequencies. The expected insulator to metal transition is found at optical frequencies, but at low frequencies an insulator-to-insulator transition occurs. Optical switching at both T < T_c and T > T_c is nearly independent of doping level and grain size. In contrast dc properties in both phases are quite sensitive to both factors. The band gaps predicted by optical and dc data differ, and densities of states change with doping level. Lattice or electron dynamics alone cannot yield such behaviour, but it can arise if there is a transient phase change. The way doping and grain size can support such a phase is discussed. Only individual nanograins need to switch phases coherently to explain data, not the whole sample. Resistance as a function of composition across the transition was derived using effective medium compositional analysis of optical data at temperatures in the hysteresis zone. Expected percolation behaviour does not arise in such an analysis, with the observed thresholds different when heating and cooling, and they occur at temperatures which differ from the usual T_c values.

The migration of electronic excitation energy between individual particles is a well-studied phenomenon. The ability to exert optical control over this transfer of energy is the subject of much recent research, and it forms the basis for a potential all-optical switching device. In detail, near-field energy transfer from an excited donor nanoparticle (following previous light absorption) to an acceptor particle can, under suitable conditions, be activated or deactivated by the input of a non-resonant laser beam, i.e. optical switching action occurs. It is envisaged that an all-optical device utilizing the described mechanism will involve nanoparticles contained within thin-film deposits on a pair of parallel substrates. Nanolithography is the technique offering the best prospects for the deposition and tailoring of nanoparticles within each optically active layer. This paper gives a theoretical analysis of the non-linear response mechanism, termed optically controlled resonance energy transfer (OCRET). The concept of transfer fidelity, signifying the accuracy of mapping input to designated output, is introduced and its key determinants are identified. Analysis shows that, at reasonable levels of laser intensity, cross-talk to unsought destinations can be effectively extinguished. The advantage of constructing these donor and acceptor thin-film layers around an ultra-thin spacer material (which is suitably transparent) is discussed, and potential applications beyond simple switching are outlined, including logic gates and optical buffers.

Oxide semiconductors are essentially stable and environmental-friendly materials as well as possessing unique multifunctional properties in conjunction with ultraviolet (UV) to deep UV (DUV) optical functions. Among them ZnO and Ga₂O₃, having the bandgaps of about 3.3 and 4.9eV, respectively, are the promising candidates for exploring their UV applications. This paper reports recent advances of ZnO and Ga₂O₃ semiconductors focusing on their UV to DUV optical functions and device applications. Since ZnO has reached to the actual application stage and future development of the growth with chemical vapor deposition (CVD) is now strongly requested for mass production, here we introduce a novel CVD growth technique, that is, ultrasonic spray assisted CVD, allowing safe and low-cost growth of high quality ZnO-based films. Homoepitaxy on ZnO substrates resulted in step-flow growth, which has hardly been achieved by metalorganic CVD. Ga₂O₃ is expected for its DUV functions being supported by the availability of Ga₂O₃ bulk substrates. We show the potential applications of Ga₂O₃ substrates for highly sensitive DUV photodetectors as well as homoepitaxial step-flow growth of Ga₂O₃ thin films by molecular beam epitaxy.

Many applications require the ability to image a scene in several different narrow spectral bands simultaneously. Absorption filters commonly used to generate RGB color filters do not have the flexibility and narrow band filtering ability. Conventional multi-layer dielectric filters require control of film thickness to change the resonant wavelength. This makes it difficult to fabricate a mosaic of multiple narrow spectral band transmission filters monolithically. This paper extends the previous work in adjusting spectral transmission of a multi-layer dielectric filter by drilling a periodic array of subwavelength holes through the stack. Multi-band photonic crystal filters were modeled and optimized for a specific case of filtering six optical bands on a single substrate. Numerical simulations showed that there exists a particular air hole periodicity which maximizes the minimum hole diameter. Specifically for a stack of SiO₂ and Si₃N₄ with the set of filtered wavelengths (nm): 560, 576, 600, 630, 650, and 660, the optimal hole periodicity was 282 nm. This resulted in a minimum hole diameter of 90 nm and a maximum diameter of 226 nm. Realistic fabrication tolerances were considered such as dielectric layer thickness and refractive index fluctuations, as well as vertical air hole taper. It was found that individual layer fluctuations have a minor impact on filter performance, whereas hole taper produces a large peak shift. The results in this paper provide a reproducible methodology for similar multi-band monolithic filters in either the optical or infrared regimes.

Wave propagation in thin nanostructured films in the low frequency regime is studied. By means of a two-scale analysis, it is shown that the medium can be homogenized, i.e. described by effective electromagnetic parameters. The effective permeability and permittivity are obtained by solving a set of partial differential equations. A numerical aproach based on the Fourier Modal Method is proposed in order to solve these equations.

We construct an external cavity diode laser (ECDL) comprising structurally left-handed chiral sculptured-thin-film (STF) mirrors for pure circular-polarized (CP) emission, and observed single mode, left-handed CP lasing performance. The extinction ratio of CP output was found to increase rapidly near the threshold of the injection-current for the laser diodes.

Surface waves (SWs) are localized waves that travel along the planar interface between two different mediums when certain dispersion relations are satisfied. If both mediums have purely dielectric constitutive properties, the characteristics of SW propagation are determined by the anisotropy of both mediums. Surface waves are then called Dyakonov SWs (DSWs), after Dyakonov who theoretically established the possibility of SW propagation at the planar interface of an isotropic dielectric and a positive uniaxial dielectric. Since then, DSW propagation guided by interfaces between a variety of dielectrics has been studied. With an isotropic dielectric on one side, the dielectric on the other side of the interface can be not only positive uniaxial but also biaxial. DSW propagation can also occur along an interface between two uniaxial or biaxial dielectrics that are twisted about a common axis with respect to each other but are otherwise identical. Recently, DSW propagation has been studied taking (i) uniaxial dielectrics such as calomel and dioptase crystals; (ii) biaxial dielectrics such as hemimorphite, crocoite, tellurite, witherite, and cerussite; and (iii) electro-optic materials such as potassium niobate. With materials that are significantly anisotropic, the angular regime of directions for DSW propagation turns out to be narrow. In the case of naturally occurring crystals, one has to accept the narrow angular existence domain (AED). However, exploiting the Pockels effect not only facilitates dynamic electrical control of DSW propagation, but also widens the AED for DSW propagation.

In this paper we report results on the synthesis, characterization and photoconductivity behaviour of amorphous and nanocrystalline ZnO/TiO₂ thin films. They were produced by the sol-gel process at room temperature by using the spin-coating method and deposited on glass substrates. The ZnO/TiO₂ films were synthesized by using tetrabutyl orthotitanate and zinc nitrate hexahydrate as the inorganic precursors. The samples were sintered at 520°C for 1 hour. The obtained films were characterized by X-ray diffraction (XRD), optical absorption (OA), infrared spectroscopy (IR) and scanning electronic microscopy (SEM) studies. Photoconductivity studies were performed on amorphous and nanocrystalline (anatase phase) films to determine the charge transport parameters. The experimental data were fitted with straight lines at darkness and under illumination at 310 nm, 439 nm and 633 nm. This indicates an ohmic behavior. The Φμτ and Φl₀ parameters were fitted by least-squares with straight lines (nanocrystalline films) and polynomial fits (amorphous films).

Amorphous and nanocrystalline SiC films enriched by oxygen were deposited by a PECVD technique using methyltrichlorosilane as a gas-precursor at substrate temperature in the range of 200-350 °C. X-ray diffraction (XRD) of the film deposited at 350°C exhibited the presence of SiC nano-crystallites. In this film the bright blue photoluminescence (PL) with spectrum that has a double-peak structure at 415 and 437 nm was obsearved at room temperature. The film was annealed at 650 and 850 °C in vacuum. Annealing at 650 °C strongly enhanced blue-white photoemission with maximum intensity around 470 cm^-1. Moderate annealing was found to lead to strengthening the C-H, C-C and Si-C bonds as well as to increasing of a size of SiC grains embedded in the amorphous Si:C:O:H matrix. A further increase of annealing temperature up to 850 °C caused a drop of PL. Basing on an analysis of experimental data and first principles simulations of several hydrogenated SiC and Si nanoclusters, we suggest that the blue PL in as-deposited nc-SiC:H film and related Si-based nanostructures can be assigned to the radiative recombination in a radiative center (RC) located at the nanocrystallite surface, whereas the excitation of electron-hole pares occurs in nanocrystallite cores. It follows from our calculations that O-O structural groups can be considered as a radiative recombination centers. The recombination at band tails of the amorphous Si:C:O:H tissue (or at the oxygen-related defect states in a-SiO_x, in the case of Si nanostructures) gives rise to a shoulder around 470 nm.

A new nano-structured SPR sensor was devised to improve its sensitivity. Nano-scaled silica particles were used as the template to fabricate nano-structure. The surface of the silica particles was modified with thiol group and a single layer of the modified silica particles was attached on the gold or silver thin film using Langmuir-Blodgett (LB) method. Thereafter, gold or silver was coated on the template by an e-beam evaporator. Finally, the nano-structured surface with basin-like shape was obtained after removing the silica particles by sonication. Applying the new developed SPR sensor to a model food of alcoholic beverage, the sensitivities for the gold and silver nano-structured sensors, respectively, had 95% and 126% higher than the conventional one.

In this work we present a theoretical and experimental work due to develop a performing configuration for gas-sensing through the employ of Surface Plasmon Resonance effect. Different sensing layers have been studied and tested on our optical bench assembly. Metallic (Au) and bimetallic (Ag/Au) layers have been properly designed through simulations and then have been realized through electron-beam evaporation. TiO₂ and TiO₂ - Au doped layers have been deposited on the top of some of the metallic samples. These layers were prepared by the sol gel route. This kind of material is expected to be suitable as a gas sensor for its nanosized structure and its stability. The optical bench configuration for the experimental exploitation of SPR is presented. It is based on a collimated beam, a rotational stage with a triangular prism and a single photodiode. Finally the sensing properties of the different sensing layers prepared was tested to some organic vapours. Preliminary results are presented.

In this work, we use oblique incident deposition technique to fabricate silver nanorod arrays (NRA). It is found that the orientation of nanorod growth does not obey the traditional tangent rule (empirical relation between the deposition angle and column growth angle). The maximum Ag nanorods tilt angle with respect to the substrate normal can reach to 76 deg. The Ag nanorods almost lie on the substrate and the array behaves as a polarizer. The transmittance versus the polarization direction of normal incident ray is presented in this paper. For a Ag nanorod array with thickness 220 nm and nanorod tilt angle 76 deg, the extinction ratio at wavelength 632.8 nm becomes 0.12 that is better than previous work. The extinction ratio of the polarizer would be further reduced to be less than 0.05 by arranging an isotropic Ag film between the Ag nanorod array and the substrate. On the other hand, it is interesting to show that Ag nanorod array is isotropic for normal incident ray with any polarization direction at a certain critical wavelength λ_c. In the wavelength range λ>λ_c, the maximum absorption occurs when the polarization is TM mode (electric field direction parallel to the deposition plane). In the wavelength range λ<λ_c, the maximum absorption occurs when the polarization is TE mode (electric field direction perpendicular to the deposition plane). The critical wavelengths for Ag nanorod arrays fabricated by different deposition angles are measured and analyzed in this paper.

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.

Analyses of the top-surface morphology of columnar thin films (CTFs) of silver, grown by a combination of the usual oblique-angle-deposition technique with very fast substrate rotation, confirm that silver CTFs consist of more isolated and quasiperiodically distributed nanowires for higher vapor incidence angle during deposition. The top surfaces then are well-suited for the exploitation of surface-enhanced Raman scattering and localized surface-plasmon resonance.

Magnesium is an essential mineral in the human body and has recently been studied as a bioabsorbable material for use in cardiac stents. New areas of application can be found in bone plates, bone screws, and orthopedic implants. Magnesium alone has a corrosion rate much too high for use in such applications and has been alloyed with various elements to improve corrosion resistance. The use of vapor deposition to create Mg alloys for the above applications has not been attempted although certain properties of non-equilibrium alloys, namely corrosion resistance, can be improved. Using vapor deposition the characterization of the growth of magnesium alloy thin films has been done utilizing various alloying elements, substrate temperatures, post-deposition treatments, and substrate positions. The results point towards a growth mode controlled by crystallization of the Mg. Mg Sculptured thin films (STFs) are used to demonstrate these effects and potential solutions while also providing a route to control nanoscale surface morphology to enhance cell growth, cell attachment, and absorption properties. The results of the study are presented in terms of x-ray diffraction data, microscopy analysis of growth evolution, and corrosion testing. This magnesium alloy research utilizes a dual source deposition method that has also provided insight about some of the growth modes of other alloy STFs. Engineering of surface morphology using dip coatings and etching has been used in biomedical materials to enhance certain application specific surface properties. STF technology potentially provides a path to merge the advantages of non-equilibrium alloy formation and engineering nanoscale surface morphology.