Optical Coatings

Plasma enhanced chemical vapor deposition ͑PECVD͒ is being increasingly used for the fabrication of transparent dielectric optical films and coatings. This involves single-layer, multilayer, graded index, and nanocomposite optical thin film systems for applications such as optical filters, antireflective coatings, optical waveguides, and others. Beside their basic optical properties ͑refractive index, extinction coefficient, optical loss͒, these systems very frequently offer other desirable ''functional'' characteristics. These include hardness, scratch, abrasion, and erosion resistance, improved adhesion to various technologically important substrate materials such as polymers, hydrophobicity or hydrophilicity, long-term chemical, thermal, and environmental stability, gas and vapor impermeability, and others. In the present article, we critically review the advances in the development of plasma processes and plasma systems for the synthesis of thin film high and low index optical materials, and in the control of plasma-surface interactions leading to desired film microstructures. We particularly underline those specificities of PECVD, which distinguish it from other conventional techniques for producing optical films ͑mainly physical vapor deposition͒, such as fabrication of graded index ͑inhomogeneous͒ layers, control of interfaces, high deposition rate at low temperature, enhanced mechanical and other functional characteristics, and industrial scaleup. Advances in this field are illustrated by selected examples of PECVD of antireflective coatings, rugate filters, integrated optical devices, and others.

Plasma enhanced chemical vapor deposition ͑PECVD͒ is being increasingly used for the fabrication of transparent dielectric optical films and coatings. This involves single-layer, multilayer, graded index, and nanocomposite optical thin film systems for applications such as optical filters, antireflective coatings, optical waveguides, and others. Beside their basic optical properties ͑refractive index, extinction coefficient, optical loss͒, these systems very frequently offer other desirable ''functional'' characteristics. These include hardness, scratch, abrasion, and erosion resistance, improved adhesion to various technologically important substrate materials such as polymers, hydrophobicity or hydrophilicity, long-term chemical, thermal, and environmental stability, gas and vapor impermeability, and others. In the present article, we critically review the advances in the development of plasma processes and plasma systems for the synthesis of thin film high and low index optical materials, and in the control of plasma-surface interactions leading to desired film microstructures. We particularly underline those specificities of PECVD, which distinguish it from other conventional techniques for producing optical films ͑mainly physical vapor deposition͒, such as fabrication of graded index ͑inhomogeneous͒ layers, control of interfaces, high deposition rate at low temperature, enhanced mechanical and other functional characteristics, and industrial scaleup. Advances in this field are illustrated by selected examples of PECVD of antireflective coatings, rugate filters, integrated optical devices, and others.

Traditionally, various vacuum-based processes, depending on material systems and properties, and chemical etching process have been used for producing di!erent types of anti-re#ection (AR) coating on di!erent substrate materials. In this paper, the development of sol}gel derived AR coating on di!erent substrates for various applications in the past 40 years are reviewed. These coatings possess good uniformity in thickness and properties which have met requirements for various applications. The major approaches to fabricate AR coating and their characteristics have been discussed. This paper outlines the major solution coating processes and design principles of AR coatings. Major fabrication processes used in AR coating technologies have been compared. Di!erent solution chemistries developed for producing di!erent materials for AR coating preparation have been extensively reviewed. The optical performance of di!erent types of sol}gel-derived AR coatings have been summarized and comparison to the commercial AR coating produced by traditional technologies have been discussed. The sol}gel AR coating has been shown to possess comparable or superior performance to those produced by vacuum-based processes.

A bright white organic light emitting diode (WOLED) was fabricated in which a blue light emitting host NPB was doped with a tiny yellow dopant Rubrene. The device structure was ITO/NPB:Rubrene/BCP/Alq3/LiF/Al, where NPB is N,N′-bis-(1-naphthyl)-N,N′-diphenyl-1,1′biphenyl-4,4′-diamine, Rubrene is 5,6,11,12-tetraphenylnaphthacene, BCP is 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline, and Alq3 is tris(8hydroxyquinoline) aluminum. White light emission was realized in an OLED with 2 % Rubrene doping concentration. A maximum luminance of 13550 cd/m 2 and a power efficiency of 2.8 lm/W (7.9 cd/A) were obtained in the device. The Commission Internationale De L'Eclairage (CIE) (1931) coordinates of the white emission are well within the white zone, which moves from (0.35, 0.37) to (0.33, 0.35) when the applied voltage is varied from 6 V to 14 V.

A perfect antireflection ͑AR͒ coating would remove completely the reflection from an interface between two media for all wavelengths, polarizations, and angles of incidence. The degree to which this can be achieved is investigated numerically. It is shown that wideband solutions can be found provided that layers can be deposited with refractive indices that are close to that of the low-index medium. Thus realistic solutions exist for interfaces between two solid media. Narrow-band high-angle AR solutions are also possible for polarized light and for unpolarized light in the vicinity of certain reststrahlen bands.

The high-energy/high-power section of the NIF laser system contains 7360 meter-scale optics. Advanced optical materials and fabrication technologies needed to manufacture the NIF optics have been developed and put into production at key vendor sites. Production rates are up to 20 times faster and per-optic costs 5 times lower than could be achieved prior to the NIF. In addition, the optics manufactured for NIF are better than specification giving laser performance better than the design. A suite of custom metrology tools have been designed, built and installed at the vendor sites to verify compliance with NIF optical specifications. A brief description of the NIF optical wavefront specifications for the glass and crystal optics is presented. The wavefront specifications span a continuous range of spatial scale-lengths from 10 µm to 0.5 m (full aperture). We have continued our multi-year research effort to improve the lifetime (i.e. damage resistance) of bulk optical materials, finished optical surfaces and multi-layer dielectric coatings. New methods for post-processing the completed optic to improve the damage resistance have been developed and made operational. This includes laser conditioning of coatings, glass surfaces and bulk KDP and DKDP and well as raster and full aperture defect mapping systems. Research on damage mechanisms continues to drive the development of even better optical materials. . Summary of the number and types of large aperture (~0.5 to 1.0 m) optics used on the NIF

The deposition of SnO 2 :Sb (ATO) and In 2 O 3 :Sn (ITO) transparent conducting coatings on glass substrate has been demonstrated by many techniques such as CVD, sputtering, vacuum deposition and sol-gel process. This paper presents an alternative process for the deposition of such coatings at room temperature by spin, dip and spray coating techniques using solutions prepared with crystalline nanoparticles fully redispersed in water (for ATO, ITO) or alcohol (for ITO) with solid contents up to 10±15 Vol.%, respectively. The deposited green coatings have been sintered at temperature as high as 9008C. In 2 O 3 :Sn coatings have a resistivity of 1.5 £ 10 22 V cm as sintered and 3.4 £ 10 23 V cm after annealing in nitrogen atmosphere. The resistivity of ATO single coatings shows a minimum r 1:7 £ 10 22 V cm after annealing at 5508C. SnO 2 :Sb coatings present long term stability but the resistivity of annealed ITO coatings steadily increases with time to a value three times higher. All coatings have a high optical quality with transmission in the visible range larger than 90%. q 1999 Elsevier Science S.A. All rights reserved.

Recently we performed a numerical investigation of antireflection coatings that reduce significantly the reflection over a wide range of wavelengths and angles of incidence, and we proposed some experiments to demonstrate their feasibility. We provide a theoretical description of omnidirectional antireflection coatings that are effective over a wide range of wavelengths.

Recently we performed a numerical investigation of antireflection coatings that reduce significantly the reflection over a wide range of wavelengths and angles of incidence, and we proposed some experiments to demonstrate their feasibility. We provide a theoretical description of omnidirectional antireflection coatings that are effective over a wide range of wavelengths.

Spinel oxide films containing at least two transition metal cations were found to exhibit p-type conductivity with high optical transparency from the visible to wavelengths near 15 mm. Resistivities as low as 0.003 V cm were measured on 100-nm thick rf sputter deposited films that contained nickel and cobalt. Optical spectra, Raman scattering and XPS measurements indicated the valency of nickel localized on octahedral sites within the spinel lattice determines these properties. A resistivity minimum was found at the composition NiCo O deposited from aqueous or alcoholic solutions followed by subsequent annealing at 4008C in 2 4 air. Solution deposited films richer in nickel than this stoichiometry, were always found to phase separate into nickel oxide and a spinel phase with concomitant loss in conductivity. However, the phase stability region could be extended to higher nickel contents when rf-sputter deposition techniques were used. Sputter deposited spinel films having a cobalt to nickel ratio -2 were found to exhibit the highest conductivity. Results suggest that the phase stability region for these materials can be extended through appropriate choice of deposition conditions. A possible mechanism that promotes high conductivity in this system is thought to be charge transfer between the resident di-and trivalent cations that may be assisted by the magnetic nature of the oxide film. ᮊ

Multilayer mirror coatings which reflect extreme ultraviolet (EUV) radiation are a key enabling technology for EUV lithography. Mo/Si multilayers with reflectances of 67.5% at 13.4 nm are now routinely achieved and reflectances of 70 2% at 11.4 nm were obtained with MO/Be multilayers. High reflectance is achieved with careful control of substrate quality, layer thicknesses, multilayer materials, interface quality, and surface termination. Reflectance and film stress were found to be stable relative to the requirements for application to EUV lithography. The run-to-run reproducibility of the reflectance peak position was characterized to be better than 0.2%, providing the required wavelength matching among the seven inultilayercoated mirrors used in the present lithography system design. Uniformity of coating was improved to better than 0.5% across 150 mm diameter substrates. These improvements in EUV multilayer mirror technology will enable us to meet the stringent specifications for coating the large optical substrates for our next-generation EUV lithography system.

Ion-exchange polymer membrane metallic composites (IPMC) are one of the electroactive polymers (EAP) that were shown to have potential application as actuators. The recent introduction of perfluorocarboxylategold composite with tetra-n-butylammonium and lithium cations instead of sodium made the most significant improvement of the material's electroactivity. Under less than 3 volts, such IPMC materials were shown to induce bending beyond a complete loop. The bending characteristic of IPMC offered an attractive actuation capability for a dust wiper in planetary applications and it was explored for the Nanorover's infrared camera window of the MUSES-CN mission. This joint NASA and the Japanese space agency mission, is scheduled to be launched from Kagoshima, Japan, in January 2002, to explore the surface of a small near-Earth asteroid. The application of EAP at space conditions posed a great challenge due to the harsh operating conditions that are expected and the critical need for robustness and durability. Several issues that are critical to the application of IPMC were addressed including operation in vacuum and low temperatures, as well as the effect of the electromechanical characteristics of the IPMC on its actuation capability. Highly efficient IPMC materials, mechanical modeling, unique elements and protective coatings were introduced to enhance the applicability of this EAP material. However, critical issues were identified that hamper the transition of IPMC from being considered for practical applications at this stage.

The objective of this study is to increase the visible transmittance of a low-emittance (low-e) glazing as much as possible by antireflection treatment. This has been carried out by depositing thin porous films of silicon dioxide, SiO , on both sides of a 2 commercial glazing with a pyrolytic low-e tin oxide-based coating. SiO was chosen because its refractive index makes it suitable 2 for antireflection treatment of both the uncoated glass side and the side of the tin oxide coating. The deposition of the antireflective films was performed with a dip-coating method, where the substrate was dipped in a sol-gel of silica. Two different silica solgels were used, one was manufactured in the laboratory and the other one was a commercial solution with a higher porosity. An increase of the integrated visible transmittance (T) by 9.8% points up to 0.915 was achieved for a coating produced with the vis commercial solution. Calculations of U value, g value and T for window configurations were also performed. vis

This device design approach combines sputter-deposited TiO 2 antireflection layer ͑ARL͒ and plasma-enhanced chemical vapor deposition-grown SiO x intermediate-reflector layer ͑IRL͒ in superstrate a-Si/ c-Si thin film solar cell. The loss of current from either the component cells with individual application of ARL and IRL has been recovered with their combined application. With both ARL and IRL in a-Si/ c-Si cell, ͑a͒ the top cell current and ͑b͒ the sum of top and bottom cell current increases. An initial efficiency of 11.8% ͓V oc = 1.42 V, FF= 0.74, J sc ͑top͒ = 11.5 mA cm −2 , J sc ͑bottom͒ = 11.2 mA cm −2 ͔ is achieved from such an a-Si/ c-Si cell with a total Si layer thickness less than 2 m.

Gasochromic films consist of an electrochromic layer such as WO and a very thin coating of a catalyst. Hydrogen gas is 3 dissociated on the catalyst into H atoms, which colour the electrochromic film. Bleaching is achieved with oxygen. In this paper the role of water for proton diffusion and the reaction process is discussed. Structural water is important to obtain a high proton mobility on the pore surface of the WO . During coloration, oxygen vacancies and water are produced. For films with a high 3 initial water content, the additional water produced in coloration leads to saturation of the pore surface, blocking further reactions. For films characterised by rapid proton diffusion, the water blocks the pore surface. This determines the first time constant of the coloration process. The relatively slow desorption of the water leads to a second time constant. Films with a low Ž water content show a deep coloration, which can be explained with the framework of this model. The bleaching in Ar, the . reverse reaction of the coloration in H , is incomplete and slow. This is a consequence of the water blocking the reactive surface 2 during the coloration process. The mechanism of the reaction is expressed in differential equations. Their solution agrees very well with the experimental data. ᮊ

We demonstrate the modulation of the transmission of near-infrared light through a periodic array of subwavelength apertures in Ag-VO 2 and Au-VO 2 double-layer films using the semiconductor-to-metal phase transition in VO 2 . The transmitted intensity ratio increases by a factor of 8 as the VO 2 goes from the semiconductor to the metal phase. We attribute this modulation to the switchable dielectric-permittivity contrast between the air-filled holes in the array and the surrounding VO 2 material, a conjecture that is semiquantitatively confirmed by simulation.

Colloidal crystals with three-dimensional periodicities in the refractive index have a photonic band gap ͑PBG͒ in which electromagnetic waves are forbidden. We present a method to fabricate stacked colloidal crystals containing a two-dimensional defect as a middle layer by combining vertical deposition method with the Langmuir-Blodgett ͑LB͒ technique. The defect layer introduces an impurity mode within the optical stop band, which is observed as a defect peak ͑pass band͒ in the optical density spectrum. The result shows that the combination of vertical deposition with LB technique provides a way for introducing defect modes in PBG materials.

It is well known that millimetre wave systems can penetrate poor weather and battlefield obscurants far better than infrared or visible systems. Thermal imaging in this band offers the opportunity for passive surveillance and navigation, allowing military operations in poor weather.We ...

Remote plasma enhanced chemical vapor deposited silicon nitride (Si x N y H z ), produced at high ammonia to silane flow rates ͑ammonia rich͒ shows a reduction of hydrogen during rapid thermal anneal at temperatures that exceed the deposition temperature. This H release could be either due to a ''slow'' atomic diffusion of the covalent bonded atoms between bonding sites, or to a ''fast'' molecular diffusion of hydrogen containing molecules ͑e.g., H 2 , NH 3 , SiH 4 ), which dissociate from the network before they diffuse. In order to determine the dominant mechanism, layers of deuterated and hydrogenated silicon nitride on top of a crystalline Si substrate were annealed and the development of the NH-and ND-area densities were measured with Fourier transform infrared spectroscopy. Comparison of theoretical models with the measurements showed that chemical dissociation and subsequent rapid diffusion are the dominant processes. These results were confirmed by secondary ion mass spectroscopy. The experiments indicate that the H reduction in silicon nitride antireflection coatings of solar cells is mostly due to H migration out of the system and not into the Si area and make the hypothesis that postdeposition annealing of solar cell antireflection coatings can cause H-related bulk passivation of the underlying c-Si therefore questionable.

One of the most critical tasks in the development of extreme ultraviolet lithography (EUVL) is the accurate deposition of reflective multilayer coatings for the mirrors comprising the EUVL tool. The second set (Set 2) of four imaging optics for an alpha-class EUVL system has been coated successfully. All four mirrors (M1, M2, M3, M4) were Mo/Si-coated during a single deposition run with a production-scale DC-magnetron sputtering system. Ideally, the multilayer coatings should not degrade the residual wavefront error of the imaging system design. For the present EUVL camera, this requirement is equivalent to depositing multilayer coatings that would add a figure error of less than 0.11 nm rms. In addition, all mirrors should be matched in centroid wavelength, in order to insure maximum throughput of the EUVL tool. In order to meet these constraints, the multilayer deposition process needs to be controlled to atomic precision. EUV measurements of the coated mirrors determined that the added figure errors due to the multilayer coatings are 0.032 nm rms (M1), 0.037 nm rms (M2), 0.040 nm rms (M3) and 0.015 nm rms (M4), well within the aforementioned requirement of 0.11 nm rms. The average wavelength among the four projection mirrors is 13.352 nm, with an optic-to-optic matching of 1σ=0.010 nm. This outstanding level of wavelength matching produces 99.3% of the throughput of an ideally matched four-mirror system. Peak reflectances are 63.8% (M1), 65.2% (M2), 63.8% (M3) and 66.7% (M4). The variation in reflectance values between the four optics is consistent with their high frequency substrate roughness. It is predicted that the multilayer coatings will not introduce any aberrations in the lithographic system performance, for both static and scanned images of 70 nm -dense features. Added figure error = 0.037 nm rms Added figure error = 0.032 nm rms Added figure error = 0.040 nm rms Added figure error = 0.015 nm rms

Functional coatings are used in increasingly demanding applications that require specific optical characteristics, resistance to damage and good adhesion to different types of substrate materials, including polymers. In the present work we investigate thin films fabricated by low pressure plasma-enhanced chemical vapor deposition, using a dual-mode microwave/radio-frequency ͑MW/ RF͒ plasma approach. The substrates are exposed to the principal dense microwave ͑MW, 2.45 GHz͒ plasma, while applying a RF-induced negative bias voltage. This technique provides independent control of the energy and flux of bombarding ions, and it allows one to deposit dense films at ambient substrate temperature at a high rate over large areas. We optimized the deposition process for amorphous hydrogenated silicon nitride ͑SiN 1.3 ͒ obtained from SiH 4 /NH 3 mixture. Using an average ion energy of about 150 eV, we obtained low-stress (Ͻ100 MPa) films with a refractive index of 1.89, at deposition rates around 30 Å/s. MW plasma pretreatments with different gases have been investigated in order to further enhance adhesion of the SiN 1.3 coatings on polycarbonate ͑PC͒ substrates-the highest adhesion, determined by the microscratch-and the adhesive-tape peel tests, was found when PC was pretreated in N 2 plasma. The adhesion is related to the thickness and chemical structure of the interface. In fact, spectrophotometry and x-ray photoelectron spectroscopy analysis suggest the presence of a graded interface region, up to 40 nm thick, part of which contains Si-C, Si-O-C, and Si-N-C chemical links.

We present an overview of currently available EUV multilayer coatings that can be used for the construction of solar physics instrumentation utilizing normal-incidence optics. We describe the performance of a variety of Si-based multilayers, including Si/B 4 C and new Si/SiC films that provide improved performance in the wavelength range from 25 -35 nm, as well as traditional Si/Mo multilayers, including broad-band coatings recently developed for the Solar-B/EIS instrument. We also outline prospects for operation at both longer and shorter EUV wavelengths, and also the potential of ultra-short-period multilayers that work near normal incidence in the soft X-ray region.

A fibre-optic refractive index sensor based on a long period grating (LPG) with a nanoassembled mesoporous coating of alternate layers of poly(allylamine hydrochloride) (PAH) and SiO2 nanospheres was demonstrated. PAH/SiO2 coatings of different thicknesses were deposited onto an LPG operating near its phase matching turning point in order to study the effect of the film thickness and porosity on sensor performance. Three aqueous solutions of ethanol, glucose and sucrose of different concentrations were used to allow characterization of the refractive index (RI) over a wide RI range (1.3330-1.4906). The device showed a high sensitivity (1927 nm/refractive index unit) to RI changes with a response time less than 2 s. In particular, the current study suggested that the low RI of the mesoporous film, 1.20 at 633 nm, facilitates the measurement of external indices higher than that of the cladding, extending the range of operation of LPG-based RI sensors. The ability of this device to monitor, in real time, RI changes during a dilution process is demonstrated and discussed.

The performance of many solid-state devices including emissive displays, optical sensors, integrated optical circuits, and light-emitting diodes can be improved by applying a transparent high refractive index coating (≥ 1.65) onto the light-emitting or light-sensing portion of the device. Ideally, the coating should combine the excellent durability and easy deposition of a spin-applied polymer coating with the high refractive index and optical clarity of a vacuumdeposited metal oxide coating such as titanium dioxide or zirconium oxide. While some success has been achieved in combining these very dissimilar materials to form transparent hybrid coating systems, for example, using sol-gel or nanoparticle dispersion techniques, the resulting coating systems often require complicated manufacturing schemes and have limited storage stability and reliability.

We have demonstrated an up to seven-fold enhancement of photoluminescence from silicon-rich silicon nitride film due to a single photonic crystal cavity. The enhancement is partially attributed to the Purcell effect. Purcell factor predicted by FDTD calculations is 32 for a linear three-defect cavity mode with computed quality factor of 332 and mode volume of 0.785 (λ/n) 3. Experimentally measured cavity quality (Q) factors vary in the range of 200 to 300, showing excellent agreement with calculations. The emission peak can be tuned to any wavelength in the 600 to 800 nm range. Silicon-based light sources compatible with the mainstream CMOS technology are highly desirable because they will have a low manufacturing cost relative to III/V semiconductor diodes, and it will be easier to integrate them with electronic components on the same chip. Photoluminescence (PL) from silicon-rich silicon nitride and, more commonly, oxide films with 3 to 5 nm precipitates of silicon nano-crystals (Si-nc) in the dielectric matrix, has been studied. 1,2 The luminescence is attributed to confined exciton recombination in the Si-nc or to the radiative recombination centers located at the interface between the Si-nc and the dielectric. 2 Internal quantum efficiencies can be as high as 59%, 3 and optical gain for Si-ncs has been demonstrated. 2 Confining luminescent material in an optical micro-cavity enhances the emission by restricting the resonant wavelength to a directed radiation pattern that can be collected effectively, and by reducing radiative lifetime of the on-resonance emitters due to the Purcell effect. 4,5 Reduction in radiative lifetime is particularly important for the development of lasers based on Si-ncs because it makes radiative recombination compete more favorably with non-radiative recombination processes which increase at higher pump powers. In this paper, we demonstrate light emitters based on two-dimensional (2-D) photonic crystal (PC) cavities fabricated in silicon-rich silicon nitride membrane. We used 2-D PC nanocavities because of their high Q-factor (Q) values and small mode volumes (V), since both are necessary for the Purcell effect. Planar geometry of the implementation is well suited for integration with other optical devices on a chip. The structures were fabricated starting from bare silicon wafers. At the first step, a 500-nm-thick oxide layer was formed by wet oxidation. At the second step, a 250-nmthick layer of silicon-rich silicon nitride was deposited by a chemical vapor deposition from NH 3 and SiH 2 Cl 2 gases at 850°C. Next, a positive electron beam resist, ZEP, was spun on a wafer piece to form a 380-nm-thick mask layer. Photonic crystal pattern was exposed on the Raith 150 electron beam system. After development, the pattern formed in the resist layer was transferred into the silicon nitride layer by reactive ion etching with NF 3 plasma 6 using ZEP pattern as a mask. All remaining resist was removed by oxygen

Inverse Fourier transform method has been commonly used for designing complex inhomogeneous optical coatings. Since it assumes dispersion-free optical constants, introducing real optical materials induces shifts in the position of reflectance bands in multiband inhomogeneous minus ͑rugate͒ filters. We propose a simple method for considering optical dispersion in the synthesis of multiband rugate filter designs. Model filters designed with this method were fabricated on glass and polycarbonate substrates by plasma-enhanced chemical vapor deposition of silicon oxynitrides and SiO 2 ͞TiO 2 mixtures with precisely controlled composition gradients.

Inverse Fourier transform method has been commonly used for designing complex inhomogeneous optical coatings. Since it assumes dispersion-free optical constants, introducing real optical materials induces shifts in the position of reflectance bands in multiband inhomogeneous minus ͑rugate͒ filters. We propose a simple method for considering optical dispersion in the synthesis of multiband rugate filter designs. Model filters designed with this method were fabricated on glass and polycarbonate substrates by plasma-enhanced chemical vapor deposition of silicon oxynitrides and SiO 2 ͞TiO 2 mixtures with precisely controlled composition gradients.

The effect of the coating thickness and roughness on the mechanical strength and thermally induced stress voids in nickel-coated optical fibers is theoretically and experimentally investigated. Seven samples of nickel-coated optical fibers with identical fiber length but different coating thickness are prepared using electroless plating method. The thickness of the nickel coating is controlled by the plating time, with the thicknesses being 35, 65, 119, 218, 308, 419 and 565 nm, respectively. The mechanical and thermal stresses in these nickel-coated optical fibers are analyzed. The atomic force microscope measurement reveals that the roughness of the nickel coating is unchanged when the coating thickness is not larger than 65 nm. However, as the coating thickness is not less than 65 nm, the coating roughness increases with increasing the coating thickness. To increase the tensile strength of the nickel-coated optical fiber, the coating thickness should be not less than 65 nm, and the surface roughness of the nickel coating should not exceed 2.93 nm. Alternatively, if the coating thickness is in the range of 35 to 218 nm, thermally induced stress voids are less found in the nickel coatings. However, if the coating thickness is in the range of 308 to 565 nm, the number of thermally induced stress voids increases with increasing the coating thickness. To minimize these voids, the surface roughness of the nickel coating should also be decreased.

The equipment and methods used to produce wide-angle antireflection coatings based on Reststrahlen materials are described. The optical constants of the coating materials used in the construction of the multilayers were determined by spectrophotometric ellipsometry and are compared with the literature values. The measured performance of an experimentally produced antireflection coating is compared with the expected calculated performance. The reflectance is low over a wide range of angles, but only in the narrow-wavelength region at which the refractive index of the Reststrahlen material is close to unity.

As immersion nanolithography gains acceptance for next generation device applications, experimental data becomes increasingly important. The behavior of resist materials, fluids, coatings, sources, and optical components in the presence of a water immersion media presents conditions unique compared to convention "dry" lithography. Several groups have initiated fundamental studies into the imaging, fluids, contamination, and integration issues involved with water immersion lithography at 193nm. This paper will present the status and results of the next stage of the development efforts carried out at RIT. The status of two systems are presented; a small field projection microstepper utilizing a 1.05 catadioptric immersion objective lens and a 0.50 to 1.26NA interferometric immersion exposure system based on a compact Talbot prism lens design. Results of the fundamental resolution limits of resist materials and of imaging optics are presented. Additionally, an exploration into the benefits of increasing the refractive index of water is addressed through the use of sulfate and phosphate additives. The potential of KrF, 248nm immersion lithography is also presented with experimental resist imaging results.

In this contribution the application of Optical Coherence Tomography (OCT) for non-invasive structural imaging of easel paintings will be presented. Since the technique permits imaging semi-transparent layers accessible for infrared light, the varnish and glaze layers are usually under investigation. The major emphasis will be laid on application of OCT to resolving specific conservation problems, arising during the restoration process. The examples of imaging multilayer varnishes and subsequent alterations will be given and the application of these images for authentication of inscriptions will be discussed. Since the thickness of imaged layers may be directly measured with OCT in completely non-destructive, quick and convenient way as many times as necessary, the application of the technique to generation of varnish thickness maps will be presented.

We present experimental results on the development and testing of the extreme ultraviolet (EUV) reflective multilayer coatingsthat will be used in the Atmospheric Imaging Assembly (AIA) instrument. The AIA, comprising four normalincidence telescopes, is one of three instruments aboard the Solar Dynamics Observatory mission, part of NASA's Living with a Star program, currently scheduled for launch in 2008. Seven different multilayer coatings will be used, covering the wavelength region from 93.9 to 335.4 Å.

The reflectance effectiveness of a multilayer depends strongly on the stack properties ͑thickness, roughness, and density of each layer͒ and can be directly tested by means of x-ray reflectivity scans at definite photon energies. The reflectivity curves are also a powerful tool for the in-depth, nondestructive characterization of the stack structure: The complex task of extracting the stack parameters from reflectivity curves can be achieved via a suitable best-fitting computer code based on a global automatic optimization procedure. We present the computer-assisted layer-by-layer analysis of the characteristics of Ni/ C, Pt/ C, and W / Si multilayers, based on x-ray reflectivity scans performed at 8.05 and 17.45 keV. In order to verify the correctness of the code predictions, we present also a comparison of the computer model with the transmission electron microscope profiles of the same multilayer samples.

MgF 2 is a current material for the optical applications in the UV and deep UV range. Nevertheless, modern applications still require improvement of the optical and structural quality of the deposited layers. In the present work, the composition and microstructure of MgF 2 single layers grown on Si [100] substrate by physical vapour deposition (PVD) and ion beam sputtering (IBS) processes, were analyzed and compared. Experiments were carried out using X-ray photoelectron spectroscopy (XPS) in depth pro®le, grazing angle X-ray diffraction (XRD) and transmission electron microscopy (TEM). Both layers exhibited a good stoichiometry and a low level of contamination. The sample grown by IBS revealed a more homogeneous and regular columnar microstructure than the other one. q

Hafnium oxide (HfO 2 ) has attracted much interest as high-k material of choice for gate oxide replacement in future CMOS technologies and for its use in optical coating technology. The determination of optical properties, like refractive index and bandgap, is focus of intense research, since the optical constants of HfO 2 depend on the physical microstructure and the deposition methods and conditions. In the present study optical characterization of very thin HfO 2 films deposited by plasma ion assisted deposition and annealed at different temperatures is carried out. The characterization is performed using ellipsometric measurements in the spectral range from 1.5 to 8 eV and by using the Tauc-Lorentz and Cody-Lorentz dispersion models. In addition, direct inversion of the ellipsometric data is also carried out. The combination of the Cody-Lorentz model with Urbach tail results in the best description of the data and enables to determine meaningful parameters. On the other hand, the direct data inversion is shown to be useful to provide additional information like the presence of subgap absorption peaks and points out features associated to the crystallinity of the material.

Amorphous hydrogenated silicon nitride, oxide and oxynitride films are deposited by plasma-enhanced chemical vapour deposition (PECVD) using a dual-mode microwave/radio-frequency (MW/RF ) plasma system. Optical filters are prepared by varying the film composition either abruptly (discrete, homogeneous multilayer structure) or continuously (graded-index, inhomogeneous structure). The coatings are characterised both optically, by spectrophotometry and spectroscopic ellipsometry, and mechanically, with depth-sensing indentation and low-load microscratch testing. A comparison is made between the properties of the homogeneous multilayer and the inhomogeneous multilayer structure with the corresponding optical performance. This multiple technique approach for characterisation was proved to be efficient for analysis of the optical and mechanical behaviour of coatings, and it provides a possibility for optimising the deposition process. It is demonstrated that the graded system exhibits a higher mechanical strength and a better toughness than the discrete structure.

We have developed a new depth-graded multilayer system comprising W and SiC layers, suitable for use as hard X-ray reflective coatings operating in the energy range 100 -200 keV. Grazing incidence X-ray reflectance at E=8 keV was used to characterize the interface widths, as well as the temporal and thermal stability in both periodic and depth-graded W/SiC structures, while synchrotron radiation was used to measure the hard X-ray reflectance of a depthgraded multilayer designed specifically for use in the range E~150 -170 keV. We have modeled the hard X-ray reflectance using newly-derived optical constants, which we determined from reflectance-vs-incidence angle measurements also made using synchrotron radiation, in the range E=120 -180 keV. We describe our experimental investigation in detail, compare the new W/SiC multilayers with both W/Si and W/B 4 C films that have been studied previously, and discuss the significance of these results with regard to the eventual development of a hard X-ray nuclear line telescope. * Periodic W/SiC multilayers containing N=300 bilayers, with periods in the range d=2.15-0.65 nm, were deposited as described above. The relative W-layer thickness was fixed at Γ=d W /d=0.4 in all cases. XRR measurements were made using a 4-circle X-ray diffractometer having a sealed-tube Cu source and a Ge (111) crystal monochromator 640

It is shown from both a phenomenological study and exact modeling that the reason for the experimentally observed substantial ͑a few angstroms or nanometers͒ separation in wavelength between the maxima of the inside ͑negative numbered͒ and outside ͑positive numbered͒ diffraction orders of a multilayer-coated grating, operating at near normal incidence and close to the Bragg condition in the soft-x-ray and extreme-ultraviolet ͑EUV͒ regions, is related to the different angles of deviation of the orders. This wavelength separation is also a feature of uncoated diffraction gratings, although not clearly noticeable. The widely used approximate approach for calculating the absolute efficiency, the product of the relative grating efficiency and the reflectance of its multilayer coating, has until recently been considered accurate enough for the analysis of soft-x-ray and EUV near-normal-incidence multilayer-coated gratings. The inapplicability of this approximation for the analysis of the precise positions and shapes of the efficiency curves for the inside and outside orders, despite the small ratios of wavelength and groove depth to period and the small angles of incidence, is demonstrated using gratings with realistic groove profiles and operating in the EUV region. The rigorous modified integral method ͑MIM͒, which is a variant of boundary integral equation methods and is designed for the calculation of the efficiency of multilayer gratings with arbitrary layer thicknesses and boundary shapes ͑including microroughness͒ and over a wide wavelength range, is proposed in a general operator formalism. An analysis of a derived simple phenomenological expression and the exact numerical study indicates that the spectral separation between the inside and the outside orders grows with increasing either wavelength, angle of incidence, groove frequency, or diffraction order number ͉m͉. The efficiency modeling carried out with the commercial program PCGRATE-SX, based on the MIM, gave not only the exact values of the spectral separation between the inside and outside orders of Mo 4 Ru 6 / Be, Mo/ Si, and Mo/ Y multilayer-coated gratings with various real groove profiles measured using atomic force microscopy ͑AFM͒ but also good agreement with synchrotron radiation measurements, including high orders as well. To determine the shapes and positions of efficiency curves in the soft-x-ray-EUV range of close to normal-incidence bulk and multilayer-coated gratings with real groove profiles ͑measured by AFM͒, one should use codes based on rigorous electromagnetic theory such as the MIM. The modeling is important for developing high efficiency and dispersion gratings for high-resolution spectroscopic studies of laboratory, solar, and astrophysical radiation sources.

In this study, optical coatings were investigated as substitutes for the coverglass on flexible thin-film space solar cells. The inherent low emissivity of copper-indium-gallium-diselenide (CIGS) thin-film solar cells was increased using optical coatings for thermal balance in space. Evaporated silicon dioxide (SiO 2 ) and an additional aluminum oxide (Al 2 O 3 ) coating on the CIGS solar cell increased the emissivity from 0.18 to 0.77. Higher emissivity was realized with the Al 2 O 3 /SiO 2 double-layer coating than with the SiO 2 single-layer coating. The straightforward double-layer coating gives the CIGS solar cells appropriate radiative properties for keeping the cell within a permissible temperature range in space.

This letter demonstrates the ability to fabricate porous silicon through the nanoscale pores of an anodized alumina template formed on a silicon substrate. The alumina template acts as a protective coating on the porous silicon surface increasing its mechanical integrity, thus eliminating the need for delicate handling that is usually required for this material system. The optical properties of the porous silicon formed through the template show characteristics similar to that of normally formed porous silicon. In addition, the porous silicon optical properties show very little degradation with time; the alumina coating is believed to contribute to this improved stability. The results are significant and can increase the likelihood of commercial applications of this material.

Current research work on the development of automated microrobot-based nanohandling stations (AM-NSs) using the probe of an atomic force microscope (AFM) as an endeffector is presented. The manipulation of individual multiwalled carbon nanotubes (MWCNTs) and the characterization of biological objects, as for instance cells or ligand-receptor bindings are aspired applications. For this reason, the developed AMNSs have to be integrated both into a scanning electron microscope (SEM) for the nanomanipulation of carbon nanotubes (CNTs) and into an optical microscope for the cell characterization. Such an AMNS combines different micro-and nanomanipulators, each offering three degrees of freedom, in order to perform the coarse and fine positioning between object and endeffector. Piezo-resistive AFM probes are applied as endeffectors allowing to measure the acting forces and to realize force feedback for the station's control system. First, investigations have been carried out by bending MWCNTs and calculating their Young's modulus. Electrically conductive adhesives (ECAs) have been developed for the microelectronics industry, and their mechanical properties have to be determined. Therefore an AMNS for the mechanical characterization of thin ECA coatings by nanoindentation inside an SEM is presented as well, showing first experimental results. The three application areas shown in this paper will provide the basis for using the considered materials in MEMS/NEMS-and biosensor-devices.

A room temperature spraying technique was developed for the deposition of transparent conducting sol-gel ATO (antimony doped tin oxide, SnO :Sb) coatings, based on an 0.2 M solution of SnCl in 1-propanol with 5 mol.% SbCl and a mixture of 2-2 2 3

The use of multilayer reflection coatings has proven to be an effective means for improving the efficiency of soft Xray and extreme ultraviolet gratings. These techniques have recently been extended to e-beam-patterned binary blazed substrates. Here we present further refinement of the e-beam-patterned substrate method, demonstrating near normalincidence reflection efficiencies as high as 41% into the first-diffracted order.

SP Vernon, PA Kearney, W. Tong, S. Prisbrey, C. Larson, CE Moore, F. Weber, G. Cardinale, PY. Yan, S. Hector ... This paper was prepared for submittal to the 18th Annual BACUS Symposium on Photomask Technology and Management Redwood City, CA September 16-18, 1998

The absorption coefficient of composite films consisting of niobia (Nb 2 O 5 ) and silica (SiO 2 ) mixtures is studied for photon energies around the band gap. The films were deposited by co-evaporation and their composition was varied by changing the ratio of deposition rates of the two materials. Both, as-deposited and thermally annealed films were characterized by different techniques: the absorption coefficient was determined by spectrophotometric measurements and the structural properties were investigated using infrared spectroscopy, transmission electron microscopy and X-ray diffraction. The correlation between the variations of absorption properties and film composition and structure is established. The absorption coefficients determined experimentally are compared with the results derived from effective medium theories in order to evaluate the suitability of these theories for the studied composites.

Nanoporous poly(methylsilsesquioxane) (PMSSQ) films prepared by the sacrificial-porogen (pore generator) approach have been demonstrated as potential antireflection coatings. The simplicity of film preparation, tunability of the refractive index and excellent control of ...