To develop porous Si as substrate for better quality GaN layer
In this work, we prepare porous Si substrates via anodic etching process. The etching parameters such as time and current would be optimized for the best porous substrate, which is defined by having high porous density. The estimated average of porous density of the substrate is determined through the observation via scanning electron microscopy (SEM). After that, a thin GaN film is deposited onto the best porous Si substrate, using RF-sputtering machine. The grown layer is then will be characterized by photoluminescence (PL), X-ray diffraction (XRD) and Hall-effect measurements. As a comparison, we also grow and characterize a thin GaN on non-porous Si substrate, with the adoption of AlN buffer layer.
Growth of crack-free hexagonal GaN films on Si(100)
Hexagonal GaN films have been grown on Si(100) substrates by employing a sputtered AlN buffer layer followed by another high-temperature metalorganic chemical vapor deposition (MOCVD) grown AlN buffer layer. The highly oriented structure of sputtered AlN provides a hexagonal template for subsequent AlN and GaN growth. The GaN films are evaluated by transmission electron microscopy, selected area electron diffraction, x-ray diffraction, and photoluminescence and exhibit a purely hexagonal columnar structure. The orientation of the GaN columns depends on the thickness of both the sputtered AlN buffer layer and the MOCVD grown AlN buffer layer. The surface of GaN films is shiny and crack free up to a thickness of 2 μm studied in this work.
Measuring Sheet Resistances of Dielectrics Using Co‐Planar Hydrogel Electrochemical Cells with Practical Applications to Characterize the Protective Quality of Paints on Sculptures
Electrical properties of thin dielectric films at the solid-liquid phase boundary are an important performance characteristic of many devices, coatings and sensors. In this paper, co-polymeric hydrogels of polyacrylic acid co-sulfonic acid, swollen with a salt solution to act as the solid electrolyte, were used to assess interfaces using electrochemical impedance spectroscopy (EIS) in a co-planar geometry. Silane-modified glasses were characterized by the co-planar hydrogel EIS cell and found to be distinguishable based on their surface monolayer chemistry. EIS measurements were also made on primed and painted metal substrates, using both test panels and an outdoor sculpture, Tony Smith's Stinger. The panels were then exposed to accelerated and outdoor weathering and showed degradation on the surface paint layers, which was observable electrochemically using EIS and confirmed visually by SEM. Electrochemical spectral features were compared between data from a standard paint-test cell versus this co-planar hydrogel cell; both cell types were able to measure coating capacitance, providing useful information about the condition of the bulk coating. Yet, sheet resistance (Rs) was a spectral feature seen only by the co-planar hydrogel cell. Thus, it can be concluded that the use of such co-planar hydrogel cells can provide an earlier warning sign to coating degradation and such cells provide a new type of spectral information that is not assessable by the standard geometry.