A new nano-diamond based mechanical polishing process has been developed and optimized for polishing super hard materials such as SiC, sapphire and diamond samples. The nano-diamond based process uses specially engineered nano-diamond particles that has ability to react with super hard materials when used for polishing. Such a reactive nano-diamond process leads to removal rates of about an order higher than the base particles and yields ultra-smooth surfaces (RMS <0.5nm) on the super hard materials along with very low sub-surface damage. The process yielded surface roughness less than 1 nm for silicon carbide, sapphire and diamond materials. The process has been studied for single crystalline, poly-crystalline and composite materials. The removal rates for different materials with the newly developed nano-diamond process compared to base nano-diamond particles and the surface finish obtained with the use of atomic force microscope, optical interferometer and tropel flat master will be presented. The mechanism of nano-diamond process will be explained in the conference.
A new reactive chemical mechanical polishing process has been developed and optimized for polishing CVD SiC mirror samples. The studies show that the abrasives, chemical nature of the slurry, and other additives play an important role in the material removal rate and surface finish of the SiC mirror. The use of different abrasive types and sizes resulted in differing roughness and removal rates. The smaller abrasives created surface defectivity or higher roughness. This can be explained by different polishing rates of different orientations of SiC grains, resulting in the grain enhancement. Under optimal conditions with appropriate abrasive particles, roughness RMS as low as 0.2 nm was achieved on CVD SiC samples. The process also did not show any scratch-like features in the optical interferometry measurements.
Sapphire is uniquely suitable for sensor windows of electro-optical systems due to its high transparency, high mechanical strength, and chemical inactivity. Unfortunately, these same characteristics also cause polishing of sapphire windows to be extremely difficult and slow. Hence the challenge is to develop a process for affordable production of large area sapphire windows with low-roughness, low-stress and without surface and subsurface damage. Here we report a novel rapid chemical mechanical polishing process that increases the material removal rate during polishing of sapphire by greater than twofold over conventional processes. Such a process can also produce angstrom level surface finish.
Thin Y2O3 films were directly grown on (100) Si substrates by the pulsed laser deposition technique. It has been found by high resolution cross-section transmission electron microscopy, x-ray reflectometry and x-ray photoelectron spectroscopy (XPS) that at the interface between Si and the grown layer, an interfacial layer always formed. Depth-profiling and angle-resolved XPS investigations showed that this layer consists of a mixture of substoichiometric SiOx(x<2) and the deposited Y2O3 layer, without forming an yttrium silicate. The thickness of this interfacial layer depended on the oxygen pressure and temperature used during the deposition. The main oxygen source for its formation is the physiosorbed oxygen which is trapped inside the grown layer during the laser ablation process. When the thickness of this low-k SiOx was reduced by decreasing the oxygen pressure during laser ablation below the optimum value, a marked degradation of the electrical properties of the structure was noticed.
The surface morphology of single crystal (100) Si wafers irradiated by 266 nm and 1064 nm laser pulses emitted by a solid state Nd:YAG laser has been investigated. The morphology of the bottom of craters remained flat and almost featureless after 266 nm single or multipulse laser irradiation up to the maximum fluence of 18 J/cm2 used in this study. The rims of the craters showed signs of radial liquid flow but it was apparent that the vaporization process was confined to the surface region. A different morphology was observed on the bottom of the craters formed by the 1064 nm wavelength laser pulses. Because this wavelength is absorbed in volume, (alpha) <104cm-1, a rather thick liquid Si pool formed at the surface. For laser fluences higher than 3-5 J/cm2 evidence of boiling sites were observed on the bottom of the crater, especially for multipulse irradiation. An evolution of surface morphology, from waves towards deep cavity was observed with the increase of pulse number. By analyzing the cavity formation mechanisms, their density and shape, we suggest that they were induced by heterogeneous boiling and not homogeneous boiling.
The crystallinity, stoichiometry and optical and electrical properties of thin Y2O3, ZnO and Ba0.5Sr0.5TiO3 films grown using an in situ ultraviolet (UV)- assisted pulsed laser deposition (UVPLD) technique have been studied. With respect to films grown by conventional PLD under similar conditions but without UV illumination, the UVPLD grown films exhibited better quality, especially for lower substrate temperatures. They also contained less physisorbed oxygen than the conventional PLD grown layers. These improvements can be explained by the action of several factors. Firstly, deep UV photons and ozone ensure a better in situ cleaning of the substrate. Secondly, the presence during the ablation-growth process of more reactive gaseous species like ozone and atomic oxygen formed by photodissociation of molecular O2 promotes the oxygenation of the films. Thirdly, absorption of UV photons by adatoms could result in an increased surface mobility. All these factors have a beneficial effect upon crystalline growth, especially for moderate substrate temperatures, where the thermal energy available for the process is rather limited.
Indium tin oxide (ITO) films were grown on (100) Si and Corning glass substrates by an in situ ultraviolet-assisted pulsed laser deposition (UVPLD) technique. The most important deposition parameter for the growth of high transparent and conductive ITO films was found to be the oxygen pressure used during the deposition. Films grown under low oxygen pressure were brown and exhibited low optical transmittance and high resistivity. For a target- substrate distance of 10.5 cm, which ensured a uniform film across 2.5 cm, the optimum oxygen pressure to obtain the lowest electrical resistivity was found to be around 10 mTorr. For higher oxygen pressures, the optical transmittance was a little bit higher but a significant increase of the electrical resistivity was noticed. X-ray photoelectron spectroscopy showed that ITO films grown in the 5-20 mTorr range were fully oxidized, without any measurable metallic content. Films grown at room temperature were amorphous regardless of the oxygen pressure used.
Most commercial diamond synthesis processes involve some form of chemical vapor deposition (CVD) which results in heterogeneous nucleation on the surface of window or dome materials. Generally, these processes have relatively long deposition times driven by the slow CVD kinetics. An alternate method called DIACERTM uses an aqueous seed crystal dispersion applied to the window substrates prior to CVD. These seed crystals reduce nucleation times and speed CVD deposition rates. Thicker coatings can be produced by repeating the seeding/CVD cycle until the required thickness is achieved. This paper reviews DIACERTM coating results on silicon substrates. Scanning electron microscopy and atomic force microscopy images of images of the coatings are presented. IR transmission results are presented both before and after sand and rain erosion exposures. The results of this testing will show DICERTM coatings to durable for the protection of silicon substrates after exposure to severe sand environments.
A model to estimate plasma absorption during deposition of thin films has been developed. In this model, the time-dependent plasma dimension is replaced by the time dependent ablation depth which can be determined by numerical simulations. A model to predict the spatial in- homogeneities in the laser-deposited films has also been developed.
The superconducting properties of YBa2Cu3O7 thin films subjected to controlled pulsed nanosecond laser irradiation were investigated. Irradiated films on (100) LaAlO3 substrates showed excellent thermal stability with the temperatures for zero resistance of approximately 90 K even after irradiation with energy densities greater than 250 mH/sq cm. The critical current density Jc of the films showed an enhancement at low energy densities, followed by a drastic decrease in Jc above a certain energy threshold. This decrease has been correlated with the melting threshold. Similar results are observed for YBa2Cu3O7 films on (100) yttria-stabilized zirconia substrates; however, the energy density was found to be much smaller.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.