Black layer coatings for the photolithographic manufacture of diffraction gratings

A black layer coating for an aluminum-photoresist interface with a reflectance less than 0.1% for 413-nm, s-polarized light incident at 25 degrees is described. It is made of space-compatible materials, and its rms roughness is less than 15 A.     

High-rate automated deposition system for the manufacture of complex multilayer coatings

A previously described automated thin-film deposition system based on rf-magnetron sputtering could deposit quite complex optical multilayer systems with good precision and with no one in attendance [Sullivan and Dobrowolski, Appl. Opt. 32, 2351-2360 (1993)]. However, the deposition rate was slow, and the uniform area on the substrate was limited. We describe an ac-magnetron sputtering process in which the same deposition accuracy has been combined with significantly better film uniformity and a fivefold or sevenfold increase in the deposition rate. This makes the equipment of commercial interest. Experimental results are presented for several difficult coating problems.     

Starting designs for the computer optimization of optical coatings

Several generic starting designs are used for the computer optimization of multilayer optical coatings. The first is a stack of many thin layers. Another, which is applicable to the needle-layer optimization method, is at least one thick layer. Examples include the following coatings: antireflection, beam divider, enhanced metallic reflector, dark mirror, and total internal reflection with prescribed differential phase shift.     

A self-templated etching route to surface-rough silica nanoparticles for superhydrophobic coatings

A simple, mild, and effective self-templated etching strategy has been developed to directly convert SiO(2) nanospheres into surface-rough SiO(2) (SR-SiO(2)) nanoparticles (NPs) by reaction with NaBH(4). Small SiO(2) NPs on the surface of SR-SiO(2) NPs can be tailored by carefully regulating the reaction time. SiO(2) nanospheres with varied sizes were etched under varied reaction conditions. Subsequently, particulate coatings were constructed on slide glass using SR-SiO(2) NPs as building blocks through the Layer-by-Layer assembly. Slide glasses just coated with two cycles of SR-SiO(2) NPs followed by calcination and hydrophobic modification exhibited superhydrophobicity because of their dual-size surface roughness.     

Comparison of algorithms used for optical characterization of multilayer optical coatings

Two algorithms used for the on-line and off-line characterization of multilayer optical coatings are experimentally compared using test samples produced by two different deposition processes and different monitoring approaches. One of these algorithms, called the triangular algorithm, demonstrates its superiority in all considered situations. We performed experiments with multilayer samples formed by high-density thin films, which allowed us to neglect possible errors in the film refractive indices and concentrate only on errors in the thicknesses of the layers of the produced coatings.     

Hard UV-curable organo-mineral coatings for optical applications

Organically-modified silicate incorporating various amounts of zirconium precursor was synthesized via a sol-gel route. The material was deposited as thin films on PMMA substrates and densified by UV-curing. Mechanical properties were measured by nanoindentation and data were recorded continuously as a function of the penetration depth during the loading-unloading cycles. Values of hardness and Young modulus were found in the range 340-440 MPa and 4-6 GPa, respectively. It was shown that these values could be tailored by varying the relative amount of zirconium in the layer. The material exhibited a very elastic behaviour that was related to its high degree of cross-linking assessed by infrared spectroscopy. Results were compared with measurements published by various groups on related materials. The mechanical and optical properties of the samples made this class of materials promising as hard coatings for optical applications.     

Properties,applications and manufacture of wear-resistant hard material coatings for tools

Wear processes during machining with cemented carbides and the effect of coatings on wear and on toughness are described. The requirements for coatings relating to optimum tool life are reviewed. Recently developed multilayer coatings with and without ceramic layers are described and examples for improvements in the tool lifetime are given. Additionally, some examples for the application of coatings for milling and chipless forming are presented.The wear-reducing effect of coatings on steel tools is described and possibilities for applications of steel tools coated using chemical vapour deposition (CVD) are elucidated. A number of examples for coated cutting and chipless forming steel tools are described.Finally, useful processes for the coating production are considered. A comparison between physical vapour deposition and CVD processes with respect to the coating temperature, the consistency and the adhesion of the coating is presented. The CVD process for economic production is considered and a suitable coating unit is outlined.     

New optimization algorithm for the synthesis of rugate optical coatings

A model of a rugate coating that takes into account production potentialities of the Leybold Syrus Pro 1100 deposition system is presented. An efficient algorithm for the synthesis of rugate coatings is proposed. Numerical results are also presented.     

Efficient refinement algorithm for the synthesis of inhomogeneous optical coatings

An efficient first-order algorithm with an exact calculation of the gradients is described and applied to the refinement of inhomogeneous dielectric thin films. Numerical results calculated at normal and oblique angles of incidence are correlated with an important mathematical theorem. It is shown that, when appropriate conditions are satisfied, the synthesis process generates binary type solutions based on two materials, including classical multilayers.     

Simulation of the flow in a coating applicator for optical fiber manufacture

A detailed numerical study is carried out on the flow field generated in an open-cup coating applicator during the coating process in the manufacture of optical fibers. This is a critical problem in the manufacture of optical fibers and poses several challenges to numerical modeling. A finite volume numerical model, using multiple domains to represent the fluid chamber and the die, is employed to obtain results on the flow. A coordinate transformation is used to model the complex geometry of the flow region. Fairly generic configurations are considered and a wide range of fiber drawing speeds, ranging up to 15 m/s, is investigated. Different boundary conditions, such as free and solid surface, at the entrance of the moving fiber are considered. Several coating materials are simulated, along with wide ranges of operating conditions and geometric designs. Though different temperatures are considered for the coating material, to obtain different fluid viscosities, the flow is considered to be isothermal. The focus is on the flow pattern and on the velocity fields in the fluid chamber and the die. Also, of interest are the resulting mass flow rate, which yields the final coating thickness, and the effects of the inlet conditions. The characteristics of the recirculating flow that arises in many cases are investigated in detail. The results are presented in terms of streamlines, velocity distributions and flow rates. The effects of geometry, coating material and die shape are investigated in detail. This is the first part of an on-going detailed study on the simulation of coating applicators for the manufacture of optical fibers in order to improve uniformity, consistency, and quality of the coating.This work was supported by the National Science Foundation, through Grants CTS-9610102 and CTS-0119356, and by the Fiber Optic Material Research Program at Rulgers University. Discussions with Professor C. E. Polymeropoulus and Dr. W. K. S. Chiu are gratefully acknowledged.