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Refractory conductive ceramics for plasmonics
Plasmonics has open the door for many technological applications such as bio-sensing, solar energy harvesting, optical metamaterials, and subwavelength communication devices in the last few decade. However, the absence of robust, high performance, high temperature stable, and low cost plasmonic materials that can be easily integrated into already established technologies, are some of the challenges. In this context, we demonstrate a computational procedure to study various refectory materials for plasmonic applications. Our detailed investigation [ACS Photonics 3, 43-50 (2016) revealed that nitride based refractory compounds possess great potential for use as high-performance alternative plasmonic compounds because of their highly metallic properties and low losses. In addition, band engineering of ternary system Ti1-xZrxN [Optical Material Express 6, 29-38 (2016)] revealed that, bulk plasma frequency, onset of interband transitions, width of bulk plasmon resonance and cross-over frequency, can be tuned flexibly in visible spectrum region. Overall, We believe that the alloy system of Ti1-xZrxN further broaden the choices of alternative plasmonic materials.
Fig. 1: Calculated absorption efficiency (left panel) and Q-LSPR (right panel).
Fig. 2: Comparison of (a) QLSPR and (b) QSPP of Ti1-xZrxN alloy system of TiN, ZrN and HfN in comparison with those of Au and Ag in comparison with those of Au and Ag
Cu3BiS3 and BaSi2 as alternative low-cost, indium-free materials for thin-film solar cells
As the global demand for energy grows, photovoltaic (PV) solar energy production is becoming increasingly important. At present Si is the leading and dominating absorber material in solar cells and has a market share of ~90% in PV technologies. However, due to high materials cost, the market share of Si based PV technologies will drop to 50% by 2020 and other alternative PV technologies such as thin-film, organic, dye-sensitized and hybrid solar cells will be in demand [1]. Among these alternative technologies, thin-film solar cells are dominating with materials like CdTe, Cu(Ga,In)Se2 and Cu2ZnSnS4 and have received much attentions during past few decades. However, the price volatility issues (In, Ga), supply issues (In, Te), and environmental issues (Cd) are of great concern in these materials for future clean and efficient technology. To overcome these issues, there has been huge interest in developing materials that contain abundant, eco-friendly, and low-cost elements. Therefore in our recent work, we discussed the importance of low-cost materials such as Cu3BiS3 [App. Phys. Lett. 102, 062109 (2013)] and BaSi2 [App. Phys. Express 7, 071203 (2014)] for solar cell applications. Employing first-principles modeling within the density function theory, we analyze the structural, electronic, optical and defect properties of these compounds and demonstrate that Cu3BiS3 and BaSi2 posses a great potential as suitable light absorber materials for application in future thin-film solar cell technologies.
Defect physics in Cu2ZnSn(S,Se)4 absorber
Understanding of defects phases along with native defects present in any material is of considerably importance since it can strongly affect the performance of the solar cell. Using a first-principles DFT approach we calculate the formation energies of native defects [Thin Solid Films 535, 318–321 (2013)] in the alloy compounds of Cu2ZnSn(S,Se)4 (CZTS) and demonstrate that S-based compounds show higher formation energy for all native defects compared to Se-based compounds. Hence, our study show that one can easily tune the defect formation energy of native defects in CZTS system by anion alloying. In addition, we also demonstrate from both theoretical and experimental standpoints [Physica Status Solidi (b) 253, 247-254, 2016 (also selected as cover page of the issue) that disorder of Cu and Zn atoms or (CuZn+ZnCu) defect pairs is in all probability the primary cause of band gap fluctuations in CZTS and this spatial variations in band gap (of the order of 200 meV) would cause large voltage losses in solar cells.
Role of Metal Contents in Friction Composites for automotive
The friction material lining applied on the sliding part of a brake- pad/shoe/block when pressed against a metallic disc or drum converts kinetic energy into the heat energy during friction process as a result of braking. The performance requirements of friction materials (FMs) are very complex and conflicting. There is an increasing demand to produce more powerful vehicles with higher performance to power ratio and better aerodynamic properties and hence, the performance expectations from the FMs have changed drastically in recent years. Therefore, development of high temperature stable FMs with good thermo-physical properties is essential to meet the aforementioned demands. During PhD studies [PhD thesis, IIT Delhi 2010 ] an extensive research work was carried out on non-asbestos organic (NAO) friction composites for automobiles applications. Formulations of brake-pads, brake linings and brake shoes were designed and developed as a part of my Ph.D. project [Wear 303, 569-583, 2013]. New concept of nano-metallic filler (copper) was first time tried in this project and showed excellent results.
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