W.D. Fan

Adhesion of diamond films on Ti-6Al-4V alloys

Diamond films have been successfully grown on Ti (Al 6%, V 4%) alloy by hot filament chemical vapor deposition (HFCVD). Different gas mixtures of methane to hydrogen and substrate temperatures were used in order to deposit high quality diamond films. Scanning electron microscopy (SEM), X-ray diffraction, Raman spectroscopy, and microhardness measurements have been used to characterize the diamond films. The results indicate that uniform high quality diamond films can be grown on the titanium alloy at a partial pressure of 2660 Pa, ratio of methane to hydrogen of 0.5-1%, filament temperature 2273 K, and substrate temperature 1073 K. The hardness of the Ti alloy is increased 30% by coating with the diamond film. The adhesion measurements indicate that diamond films grown on the Ti alloy have excellent adhesion.

Magnetic properties of BaTiO3/La0.7Sr0.3MnO3 thin films integrated on Si(100)

Two-phase multiferroic heterostructures composed of room-temperature ferroelectric BaTiO3 (BTO) and ferromagnetic La0.7Sr0.3MnO3 (LSMO) epitaxial thin films were grown on technologically important substrate Si (100). Bilayers of BTO/LSMO thin films display ferromagnetic Curie transition temperatures of ∼350 K, close to the bulk value, which are independent of BTO films thickness in the range of 25–100 nm. Discontinuous magnetization jumps associated with BTO structural transitions were suppressed in M(T) curves, probably due to substrate clamping effect. Interestingly, at cryogenic temperatures, the BTO/LSMO structure with BTO layer thickness of 100 nm shows almost 2-fold higher magnetic coercive field, 3-fold reduction in saturation magnetization, and improved squareness compared to the sample without BTO. We believe that the strong in-plane spin pinning of the ferromagnetic layer induced by BTO layer at BTO/LSMO interface could cause such changes in magnetic properties. This work forms a significant ste...

Wear resistant diamond coatings on alumina

Abstract Wear resistant diamond coating systems on alumina substrates with improved adhesion have been developed. These systems consist of single layer diamond coatings and multilayer composite diamond coatings. The multilayer diamond coating systems are made up of an embedding intermediate layer of TiC or TiN or TiCTiN deposited by laser physical vapor deposition on a first layer of diamond. A second layer of diamond is also deposited on the embedding layers. Scanning electron microscopy and Raman spectroscopy have been used to characterize the coatings. Adhesion and wear resistance of the coatings have been tested using an indentation test and an overlap polishing test. The improvement in adhesion of the composite diamond coatings with TiC embedding layer is found to be highest. Mechanisms of the adhesion and wear resistance improvement of the composite films are investigated. The improvement in adhesion is explained by the epitaxial growth of TiC on alumina, TiC and CC bondings between TiC and diamond, the small difference in the thermal expansion coefficients between TiC and alumina, and the close matching of lattice constants between TiC and diamond.

Complete vertical M-H loop shift in La0.7Sr0.3MnO3/SrRuO3 thin film heterostructures

In the current work, we have epitaxially integrated La0.7Sr0.3MnO3/SrRuO3 (LSMO/SRO) BLs with the technologically important substrate Si (100) using pulsed laser deposition. Interestingly, at 4 K, under the magnetic field sweep of ±1500 Oe, a complete vertical M-H loop shift is observed in the sample prepared with 180 nm SRO thickness, which is unusual. This vertical shift persists even up to a field sweep range of ±6000 Oe, at which point the shift disappears and a symmetrical hysteresis loop centered at the origin is observed. In contrast, at the same temperature, under the same field sweep range, we observe a normal M-H loop (no or little vertical shift) from the sample with 45 nm SRO thickness. In both the cases, the LSMO thickness was held constant at ∼100 nm. It appears that SRO moment is frozen in place in the latter case, providing a clear demonstration of the effect that biasing layer (SRO) thickness can have on the magnetic characteristics of bilayer films. We attribute this vertical shift to th...

Multilayer diamond coatings on silicon carbide

Abstract Multilayer composite diamond coatings on SiC substrates with improved adhesion and wear resistance have been developed. The coatings consist of a first layer of discontinuous diamond crystallites which are anchored to the SiC substrates by an interposing layer of TiC or TiN films. A top layer of continuous diamond film is grown epitaxially on the first layer. The diamond films and TiC or TiN films were deposited using hot filament chemical vapor depostion and laser physical vapor deposition, respectively. The diamond films were characterized by scanning electron microscopy and Raman spectroscopy. Adhesion of the diamond coatings to SiC seal ring substrates was investigated by using overlap polishing with diamond paste or by wear test against Al-12.5%Si alloy. The results show that, after introducing an interposing layer, the internal thermal stresses are reduced so that the adhesion of diamond coatings on the SiC substrates is improved significantly.

Multilayer Composite Diamond Heat Spreaders for Electronic Packaging

Heat spreader characteristics of single layer and multilayer diamond composite substrates are determined by bonding to electronic device wafers. Preparation of diamond substrates, metallization and bonding procedures to device wafers are described. Infrared microscopy imaging of the bonded device wafers is used to determine the heat spreading characteristics. Advantages associated with multilayer diamond composite heat spreaders are discussed.

Silicon Nitride Tools Coated With Tic Or Tin Composite Diamond Structures

Composite diamond coatings on Si 3 N 4 substrates have been developed to minimize stresses/strains and improve wear and adhesion properties. The coatings consist of a first layer of discontinuous diamond crystallites which are anchored to the Si 3 N 4 substrate by a second interposing layer of TiC or TiN film. A top third layer of continuous diamond film is grown epitaxially on the first layer. The diamond films and TiC or TiN films were deposited using hot filament chemical vapor deposition and laser physical vapor deposition, respectively. The TiC and TiN films were examined by X-ray diffraction. The diamond films were characterized by scanning electron microscopy and Raman spectroscopy. Adhesion of the diamond coatings was investigated using overlap polishing with diamond paste, wear against Al-12.5%Si alloy, and pull-test. The results show that after introducing an interposing layer of TiC or TiN, adhesion of diamond coatings on Si 3 N 4 substrates is improved significantly. After polishing test against diamond paste for 4 hours, only 30% of diamond was retained with single diamond coating while 80% of diamond was found with TiN composite diamond coating. The mechanism of improvement of adhesion is discussed.

Growth of Continuous Diamond Film by Hot Filament C VD Technique on SiC/TiC Pellets, Synthesized Using Combustion Synthesis

Abstract β-SiC/TiC composites were synthesized using the process of self propagating-high temperature combustion synthesis (SHS). The heat released during the exothermic reaction between the metal and the carbon powder results in the melting of silicon and the titanium into which the carbon diffuses and then (3-SiC and TiC precipitates out from the supersaturated solution. The composite was characterized using X-ray diffraction techniques, Raman spectroscopy, scanning electron microscopy and transmission electron microscopy. An attempt was made to understand the mechanism of formation of the composite. A theory is proposed for the possible mechanism based on dissolution, diffusion and precipitation from the supersaturated solution. Diamond film was then grown on the pellet by hot filament CVD technique using methane and hydrogen gas as the reactants. The deposition was conducted for a period of four hours. A continuous film of diamond was found to grow on β-SiC/TiC composite using this technique. The diam...