Silicon Nitride and Hydrogenated Silicon Nitride Thin Films: A Review of Fabrication Methods and Applications

Experimental Investigation of Milling Performance of Silicon Nitride Ceramic Subject to Different Assisted Systems

In this study, silicon nitride milling experiments are carried out using Polycrystalline Diamond (PCD) end mill rods under unassisted, hybrid-assisted (combination of laser assisted and three axis ultrasound), and laser-assisted systems to examine the cutting performance and machined surface quality of different cutting tools. The best combination of process parameters for silicon nitride composites milling are obtained using the Taguchi method. The effects of spindle speed, radial depth of cut, and feed rate on surface roughness, cutting force, edge topography, and tool wear of silicon nitride surfaces are investigated. The results reveal that hybrid-assisted produces superior surface roughness, longer tool life, fewer machining defects, and lower cutting force than unassisted. Best results of triaxial ultrasonic-assisted combined with laser on cutting performance are achieved as the ultrasonic waves help to vibrate the cutting tool and workpiece simultaneously, which helps to effectively remove chips and lowers the cutting force. When compared to unassisted milling, laser-assisted and hybrid-assisted milling improve total average surface roughness by 42% and 66%, and total cutting forces by 26% and 46%, respectively. The best processing parameters obtained in this study are high spindle speed (12,000 rpm), low feed rate (500 mm/min), and low cutting depth (0.02 mm).

Development and Evaluation of Copper Based Transparent Heat Reflectors Obtained by Magnetron Sputtering

Within the next few years climate change is likely to become a major concern for mankind. In addition, the current electronic components shortage crisis has led to an urgent need for alternative solutions in the main industry sectors (the raw materials, manufacturing, and construction industries). The current trends of research are focused on developing smart materials with functional properties, using abundant raw materials. The energy saving efforts are sustained in the glazing industries by several approaches based on dielectric-metal-dielectric multilayer structures. The use of silver to achieve a high reflectivity in near-infrared spectral range has been proposed and is already adopted as a commercially available solution. This work is focused on developing a transparent heat reflector (THR) with prefigured optical properties, using copper as a reflective layer, a material that is more abundant and cheaper than silver. The conductive copper layers obtained by the High Power Impulse Magnetron Sputtering (HiPIMS) method were interposed between two silicon nitride layers deposited by the Radio-Frequency Magnetron Sputtering (RFMS) technique. The structural, optical, and elemental composition of monolayers was investigated, qualifying each individual material for use in the multilayer structure. The time stability of films deposited on microscope glass substrates was also investigated, as an important criterion for the selection of monolayers. The obtained results revealed that the SiN_x/Cu/SiN_x with the Cu layer deposited by using a negative substrate bias of -100 V showed the most stable behavior over time. Optical modeling was performed to design a THR multilayer structure, which was successfully obtained experimentally. A maximum optical transparency as high as 75% in the visible range and a reflectivity of ~ 85% in near infrared spectral interval was confirmed for the experimentally obtained multilayer structures.

Optical Properties and Stability of Copper Thin Films for Transparent Thermal Heat Reflectors

The use of thin metallic layers at the thickness limit where transparency or spectral selectivity are achieved is gaining increased interest. The use of cheap and abundant materials is desirable in the attempt to avoid environment or economical costs. The use of Cu as a replacement for Ag as a heat reflector is one of the solutions that can be employed. The stability over time is a known issue, copper being prone to atmospheric oxidation and degradation. In this contribution, the stability of Cu obtained by magnetron sputtering is investigated, using both DC and HiPIMS processes for obtaining the Cu thin films. The bias voltage is used to obtain thin films with different properties, their time stability being investigated through the variation of spectrophotometric curves. The best performing thin films are evaluated in theoretical heat reflector structures, using SiNx of different qualities as dielectric layers to form the dielectric/metal/dielectric structure.