Aspects of thin film deposition on granulates by physical vapor deposition

Abstract

Thin film and coating technology has entered fields which may show significant deviations from classical coating applications where films are deposited on plane, sometimes large substrates. Often surfaces of small and irregularly shaped bodies have to be improved in respect to electrical, thermal or mechanical properties. Film deposition and characterization on such small substrates is not a trivial task. This specially holds for methods based on Physical Vapor Deposition (PVD) processes such as sputter deposition and its ion-and plasma assisted varieties. Due to their line of sight nature a key issue for homogenous films is efficient intermixing. If this problem is mastered, another task is the prediction and determination of the film thickness on single particles as well as on large scale ensembles thereof. In this work a mechanism capable of uniformly coating up to 1000 cm 3 of granulate with particle sizes ranging from approx. 10 μm to 150 μm by magnetron sputtering is thoroughly described. A method for predicting the average film thickness on the particles is presented and tested for several differently shaped objects like microspheres, irregular grains of sinter powder or micro diamonds. For assessing the film thickness on single particles as well as on particle ensembles several complementary methods based on optics, X-ray analysis and gravimetry are employed. Their respective merits and limitations are discussed. Finally an outlook on adapting the described technology for surface modification by plasma based reactive and non-reactive processes is given.

Aluminum Coated Micro Glass Spheres to Increase the Infrared Reflectance

“…As listed in Table 2, batches of all types of the investigated spheres were coated with different layer thicknesses of aluminum at the University of Vienna. For this purpose, a PVD process especially designed for spherical particles was utilized [21,22]. During the coating process, a strong agglomeration behavior especially for sphere type iM16K-ZF, without anti-agglomeration agent on the surface, was observed.…”

“…First the precursor aluminum trihydride dibutyl etherate is produced by reacting 3 M lithium aluminum hydride (LiAlH4, Sigma Aldrich) with 1 M aluminum chloride (AlCl3, Sigma Aldrich) in 2 × 50 mL of anhydrous dibutyl ether (Sigma Aldrich) for 120 min at room temperature (2) [21,22] The white arrows indicate either impurities resulting from the manufacturing process, or in the case of the sphere type S38HS, the additional anti-agglomeration agent. After pre-conditioning, calcium silicate nanoparticles are deposited on the surface of each sphere type.…”

“…First the precursor aluminum trihydride dibutyl etherate is produced by reacting 3 M lithium aluminum hydride (LiAlH 4 , Sigma Aldrich) with 1 M aluminum chloride (AlCl 3 , Sigma Aldrich) in 2 × 50 mL of anhydrous dibutyl ether (Sigma Aldrich) for 120 min at room temperature (2) [21,22]. The generated precursor is then separated from the byproduct lithium chloride (LiCl) by filtration and subsequently mixed with the Micro Glass Spheres (MGS).…”

“…Because of its properties as not noble metal, aluminum cannot simply be deposited by means of electroless deposition. Instead, thin films of aluminum on surfaces are mainly applied via Physical Vapor Deposition (PVD) or Chemical Vapor Deposition (CVD) methods [21][22][23]. PVD advantageously produces high quality coatings, but is limited in batch size and materials to be coated.…”

The methodologies and strategies for the development of novel material systems and coatings for applications in extreme environments − a critical review

“…Their unquestionable advantage is the complete embedding of the particles to be coated within the protective coatings. For instance, the electrolyte or the gas which permeates the suspended particles in a fluidized bed [22]. Nonetheless, often the choice of coating material is limited, for instance by the conductivity of the substrate, or by the availability of electrolytic solutions, or by the existence of a suitable precursor gas.…”