April 2007

NanoCalc-2000 Used to Measure Optical and Non-Optical Coatings
By Gerald Nitsch & Gregory Flinn

Coatings are readily perceptible in everyday life, for example, as hardness and reflection coatings on sunglasses and as anti-fog coatings on ski goggles. But, we also find coating technologies being applied in less obvious situations outside the optics industry, for example, as layers on the inside of beverage containers to protect the flavor of the contents and in medical, electronics and industrial fields to provide passivation, hardness and/or insulation to improve overall component functionality.

Ranging typically from sub-nm up to sub-mm thickness, these layers can be formed by many different processes including spin coating, vacuum evaporation, sputtering, vapor deposition and dip coating. Often termed thin films because of a propensity for being partially transparent, the layer’s exact thickness, its composition and integrity as well as its flatness and roughness are usually critical to its proper function.

Optical Characterization

Optical techniques are the preferred method for assessing thin film thickness, principally because they are accurate, non-destructive and require little or no sample preparation. One such technique employs a broad spectrum of light directed normally onto the twin surfaces of a thin film. The two reflections interfere with each other, and a modulation of the light intensity as a function of wavelength is seen in the reflected beam (white light interference). The NanoCalc-2000 from Mikropack GmbH of Ostfildern, Germany, employs this technique and is designed as a versatile and configurable system for both optical and non-optical applications.

The NanoCalc-2000 generates wavelength dependent reflectance data, a fit to this data requiring reasonable knowledge of refractive index n( l) and extinction coefficient k( l). These parameters are usually based on look-up values of material models describing n and k with a few adjustable parameters. Knowledge of these parameters means that an accurate value for absolute film thickness can be calculated.

Films from around 10 nm up to 400 µm can be measured with a resolution of 0.1 nm, the only crucial aspect being that they have some degree of transparency. Even metal films can be measured at thicknesses above 1 nm, as long as the layer is not opaque. Known parameter systems, even multilayer films comprising up to three layers, can be accurately modeled in much less than a second.

Measurement Versatility

For physically complex geometries, Mikropack has developed a range of fiber optic coupled interface adaptors. In addition to measurements on curved surfaces such as those found on reading glasses or on aspherical lenses, specific adaptors are available for accessing enclosed surfaces. Accessories for 2D topographic mapping over intermediate distances are also available. When used in conjunction with a microscope, the spatial resolution can be reduced from around 400 µm down to 1 µm, enabling measurement of the films to be used in applications, such as heart catheter balloons.

The NanoCalc-2000 can also be used to measure underlying “surface preparation” layers. For example, optical coatings are used for scratch resistance and to enhance the optical performance (reflectance, transmittance) of transparent materials in many industries including automotive plastics and eyeglass lenses, many hardcoats uses are for wear and scratch resistance, but an initial primer layer is often needed to improve hardcoat adhesion. Given proper initial estimates and material parameters, this technique is capable of measuring the thickness of these layers individually or simultaneously with the upper layer.

Accurately measuring thin films created for optical applications is usually trivial. These coatings are optically flat and homogeneous, have a high degree of transparency and usually exhibit strong reflections due to large changes in refractive index at smooth interfaces.

Non-optical coatings often exhibit the exact opposite of these characteristics, and accurate measurement is then difficult because of aspects such as weak bottom surface reflection (worsened still by poor layer transparency) and interface roughness. Both effects reduce the contrast in the interference signal, which in turn, requires more complex modeling algorithms.

Applications Diversity

A wider variety of fields can be addressed regarding partially opaque and entirely non-optical films that can be accurately modeled, whether metallic, dielectric or crystalline and amorphous semiconductor.

Typical non-optical thin film measurement applications include coatings on jewelry and furniture, aluminum films on paper and packaging, hard coatings on the inside of glass and plastic bottles, “Lotus Effect” dirt and weather resistant coatings on window glass as well as wear resistant layers on components for the watch-making industry.

Even the substrates destined for use with coatings do not need to be optically smooth. Nonetheless, measuring the thickness accurately and checking for some degree of layer integrity is still critical for many applications, for example, in removing resist layers during wafer, electronics or lithographic processing. Steel, aluminum, brass, copper, ceramic and plastic substrates also do not need to be optically smooth, and are often coated with a hard wearing diamond-like carbon (DLC) layer for industrial tooling applications.

Importantly, interface roughness can be readily modeled on the fly based on expected and actual reflectance amplitudes of a known material interface. This ability of the NanoCalc-2000, to cope with surface roughness in the measurement process greatly increases its applicability, reliability and practicality in an industrial setting.

Use in Industry

Favored chiefly for its simplicity, robustness and cost-effectiveness as a tool for wafer fab applications, this technique has since found use in countless other application fields. The large spectral range available from 250 nm (UV) to 1,100 nm (NIR), as well as roughness simulation algorithms allow the measurement not only of standard samples like oxides, nitrides and resists on ideal substrates such as silicon wafer or glass, but also the measurement of critical layers like DLC or the thickness of transparent, non-optical foils.

All of these practical characteristics, together with short measurement times and the flexible positioning of the fiber head, make this system a suited choice for integration into existing machinery and as a useful quality control tool in industrial manufacturing.

PANalytical has celebrated a milestone by completing the assembly of system number 2,000, which is destined for US Geological Survey in Denver, Colo.

“We look forward to taking advantage of the advanced features the high performance PANalytical X'Pert PRO MPD diffraction system brings to our Energy Team Geochemical Research Labs, located in Denver, Colo,” said Jamey D. McCord of US Geological Survey.

Every PANalytical X’Pert PRO X-ray diffractometer is unique, built to meet the needs of a specific customer.

“We are very proud that since the first units were introduced in 1999, X’Pert PRO has turned out to be a highly successful family of XRD systems,” said Peter Munk, marketing manager of X-ray diffraction (XRD) at PANalytical. “Those working in the field of XRD continue to be faced with new applications and technological challenges. The flexibility built into the X’Pert PRO line, which exploits our unique PreFIX concept, allows us to continue to meet their needs.”

X’Pert PRO instruments are installed on every continent, in research institutes and a growing range of industries that includes metals, minerals, plastics, pharmaceuticals and semiconductors. With recently introduced ultra-fast and high-sensitivity detector options, the system is suited for many applications, from routine characterization to in-depth research investigations.

New Stitches to be Absorbed by the Body

Patients who get stitches may never need to have them removed thanks to help from a new type of suture based on MIT research.

A biopolymer suture, recently cleared by the FDA, is made of materials the human body produces naturally, so they can be safely absorbed once the wound is healed. They are also 30 percent stronger than sutures now used and very flexible, making them easier for surgeons to work with.

The sutures were developed by Tepha, Inc., a Cambridge company working toward using the same material to produce an array of absorbable medical devices, including stents, surgical meshes and possibly a heart valve scaffold, said Simon Williams, CEO of Tepha and a former MIT postdoctoral associate.

Williams said he envisions that the new sutures will be used for abdominal closures, which are prone to re-opening, and to stitch tendons and ligaments.

The absorbable sutures are the first made from material produced by genetically modified bacteria. About 20 years ago, researchers in an MIT laboratory started swapping genes between different bacteria, hoping to achieve industrial production of desirable natural compounds synthesized by those bacteria.

The researchers focused their biopolymer engineering efforts on a group of genes that code for enzymes in a pathway that produces polyesters. Those polyesters can be broken down into metabolites naturally produced by humans, so they cause no harm when absorbed. Once the genes were identified, they could be transferred into a strain of industrial E. coli that can produce large quantities of the strong, flexible polymer.

The new suture is the first of what the researchers hope will be many medical devices made from the natural polyesters.

Original work at MIT on this technique was funded by the National Institutes of Health.

CPS Technologies, a company that designs and produces metal matrix composites, now offers hermetic microelectronic packages.

Made from materials such as Kovar, aluminum and steel, CPS’ engineered hermetic microelectronic packages enable successful communication for military, electronics, satellite and aerospace markets.

With more than 60 years of combined experience in hermetic microelectronic packaging, CPS has supplied and assembled AlSiC (aluminum silicon carbide) components for use in hermetic microelectronic packages for select customers since 1987. It now offers its hermetic microelectronic packages to the market at large.

Liquid Injection Molding Systems by Shin-Etsu Silicones Provide Adhesion Without Primer

Shin-Etsu Silicones of America, Inc., a US subsidiary of Shin-Etsu Chemical Co. Ltd., Japan, has recently introduced its KE2090 and KE2095 series Select-Hesive LIMS (Liquid Injection Molding Systems) that provide primerless adhesion to a variety of thermoplastic resins. Optimal for multi-component silicone-to-plastic molding, both products are specifically engineered to adhere to the thermoplastic substrate (plastic inserts) but not to the metal surfaces of the mold.

Engineered for both silicone and plastic molders using either insert over-molding or co-injection (2-shot) molding, the KE2090 and KE2095’s short curing time yields a chemical bond that produces a firmly integrated composite part (rigid and elastomeric). Whereas no primer or pre-treatment of the substrate is required, adhesion tests proved that the silicone tore before the adhesive bond broke; resulting in 100 percent cohesive failure.

Cost-efficiencies yielded from eliminating the intermediate operations are enhanced by the new LIMS bond strength performance under extreme conditions of high temperature (120°C), high humidity (85°C/85 percent RH) and thermal cycling (-40°C to 120°C). While both products deliver the best of these properties, each has optimal adhesion applications; KE2090 series for adhesion to PC, PBT and PPO compounds, while the KE2095 series functions with PA (6,6 nylon and 6-nylon) and PPA resins.

The new Select-Hesive LIMS product line offers hardness ranges from 30 to 70, Shore-A. A comprehensive range of physical properties and processing data is available in Shin-Etsu’s new LIMS Product Selection Guide. The advanced product meets Shin-Etsu’s standards for lot-to-lot consistency and is available in bulk drums and pails.

“Shin-Etsu’s Select-Hesive LIMS silicones provide designers and molders the means to manufacture a bi-material component in a fully automated manner by eliminating the need for hazardous priming, inconvenient pre-treatments, and costly secondary assembly operations,” said Eric Bishop, marketing manager. “This technology enhances product design, improves performance, and increases productivity.”

Anderol, Inc., a global manufacturer of specialty synthetic lubricants, recently released a new grease selection guide that is aimed at helping maintenance and operations engineers with specific grease application needs. The brochure provides a step-by-step guide to selecting the most effective grease based on application requirements and OEM specifications.

Choosing the right grease is critical to proper grease maintenance practices. Without the right grease, a production unit can experience unscheduled downtime, requiring expensive component repair costs. For proper selection, several factors must be considered including the application criteria related to environmental and mechanical conditions and OEM specifications. However, OEM grease specifications often lack clarity, leaving maintenance engineers in need for more information and guidance to choose the grease that best suits their needs.

Anderol’s grease selection guide has been developed specifically for end users involved in maintenance, repair and operations. Written in easy-to-understand language, the brochure outlines valuable information through charts and illustrations making it a useful tool. It categorizes in-depth information on application criteria, an important determinant in grease selection, such as temperature, water and chemical resistance, speed, loads, food grade requirements and wire rope applications.

The brochure also covers advantages and disadvantages of a wide variety of thickener types including lithium, lithium complex, aluminum complex, calcium, silica and inorganic gels. This information helps engineers understand the general characteristics of the product, and related compatibility issues which are critical to optimal performance and longevity of the equipment.

It is a high-grade solvent-based formulation with a light amber color and a very low odor that is safe and easy to apply in any factory or tool assembly area. It rapidly penetrates recessed areas, dries quickly and leaves a non-dimensional, soft waxy film and is compatible with all lubricants, cutting oils and hydraulic oils and acts as an ideal topcoat over black oxide and phosphate conversion coatings to seal out corrosion and provide break-in protection while enhancing the depth of color.

Corrosion is combated several ways with the product. The liquid product is thin enough to rapidly penetrate recessed areas and displace moisture out of the part. Once the moisture is gone, the film dries quickly leaving a non-oily, colorless film that resists moisture and prevents corrosion before it starts. The film has a flexible, self-healing property, to re-flow and re-coat areas that are scratched or damaged during handling. Any subsequent contact with water will cause the water to simply bead up and drain off the part.

The barrier can be applied to wet or dry surfaces and is absorbed by the part itself, enhancing part color and becoming an effective barrier against atmospheric humidity and corrosion. This property is especially useful on porous materials, such as powdered metals, cast/ductile iron, or subassemblies, and parts with blind holes or other problem parts that need better protection. The corrosion barrier is robust and long-lasting because the protective film will not drain off the part or wick off into packaging materials.

DRI Touch Amber is rated for 100 or more hours of salt spray and 600 or more hours of humidity protection.