Epitaxial Nitride Thin Film and Heterostructures: From Hard Coating to Solid State Energy Conversion

Epitaxial nitride thin films and heterostructures are one of the most celebrated class of materials not only due to their utility in fundamental materials science and device physics studies, but also for their numerous industrial applications from hard coating technology to solid-state lighting. Transition metal nitrides such as TiN and others have been utilized for decades in hard coating and tribology applications. The last two decades have also seen the emergence and dominance of GaN for solid-state lighting and power electronic applications. Though TiN, and other wurtzite III-nitride semiconductor such as GaN remain the most important nitride coating materials for a range of applications, several other rocksalt nitride thin film and superlattice heterostructures such as ScN, CrN, and TiN/(Al,Sc)N metal/semiconductor superlattices have attracted significant interests in recent years for applications in thermoelectricity, plasmonics, solar energy conversion, and in high temperature electronic, optoelectronic, and plasmonic devices. In this chapter, we present an up-to-date summary of rocksalt nitride thin film and heterostructure coating materials for their applications in energy transport and conversion research fields. The suitability and usefulness of such nitride coating materials in the most recent scientific and engineering advances related to the energy transport and conversion research fields are highlighted

Characterization of TiAlCrYN nanocomposite coatings prepared using four-cathode reactive unbalanced direct current magnetron sputtering system

In this study, approximately 1.5–2.5 μm thick, TiAlCrYN nanocomposite coatings were deposited on various substrates such as high speed steel (HSS) drill bits, mild steel and silicon by reactive magnetron sputtering. The coatings were characterized using X-ray photoelectron spectroscopy, X-ray diffraction, field-emission scanning electron microscopy and nanoindentation techniques. TiAlCrYN nanocomposite coating exhibited hardness of the order of 25 GPa. Micro-Raman spectroscopy was used to characterize the structural changes as a result of heating of the TiAlCrYN nanocomposite coatings in air (600-1000oC) and the coatings were found to be thermally stable in air up to 900oC. For the performance evaluation, the TiAlCrYN coated high-speed steel (HSS) drill bits and uncoated HSS drill bits were subjected to accelerated machining conditions. The uncoated HSS drill bits failed after drilling 50 holes, while drilling a 12 mm thick 304 stainless steel plate, whereas, the TiAlCrYN coated drill bits averaged 657 holes before failure

Deposition of TiAlSiN nanocomposite coatings using four-cathode reactive direct current unbalanced magnetron sputtering system

Surface engineering approaches are being increasingly employed for enhancing the effective life of cutting tools with a view to reduce machining costs. The ever increasing demands for high precision machining and increased cutting performance in terms of cutting speed and lifetime require wear resistant tools of large dimensional accuracy having very sharp cutting edges. In this study TiAlSiN nanocomposite coatings were deposited on high speed drill bits, mild steel, silicon substrates and tungsten carbide cutting tool inserts using a four cathode reactive direct current unbalanced magnetron sputtering system. TiAlSiN nanocomposite coatings were deposited using Ti, Al, and Si, targets in the presence of Ar and N2 plasma. Various treatments were given to the substrates to improve adhesion of TiAlSiN coatings. The coatings were characterized and tested for their tribological properties. The morphology of the as-deposited coatings was characterized using FESEM and AFM. The mechanical and the thermal stabilities were also evaluated. These coatings exhibited hardness in the range of 30-35 GPa. For the performance evaluation, the TiAlSiN coated drills were tested under accelerated machining conditions. With a drill speed 800 r.p.m and feed rate 0.08 mm/rev. the uncoated drill failed after drilling 50 holes in a 12 mm thick 304 stainless steel plate. Under the same conditions the TiAlSiN coated drills averaged 714 holes before failure. Results indicated that for TiAlSiN coated drill the tool life can be increased by a factor of more than 14

Deposition and characterization of TiAlSiN nanocomposite coatings prepared by reactive pulsed direct current unbalanced magnetron sputtering

This work reports the performance of high speed steel drill bits coated with TiAlSiN nanocomposite coating at different Si contents (5.5–8.1 at.%) prepared using a four-cathode reactive pulsed direct current unbalanced magnetron sputtering system. The surface morphology of the as-deposited coatings was characterized using field emission scanning electron microscopy. The crystallographic structure, chemical composition and bonding structure were evaluated using X-ray diffraction, energy-dispersive X-ray analysis, X-ray photoelectron spectroscopy, respectively. The corrosion behavior, mechanical properties and thermal stability of TiAlSiN nanocomposite coatings were also studied using potentiodynamic polarization, nanoindentation and Raman spectroscopy, respectively. The TiAlSiN coating thickness was approximately 2.5–2.9�m. These coatings exhibited a maximum hardness of 38 GPa at a silicon content of approximately 6.9 at.% and were stable in air up to 850 ◦C. For the performance evaluation, the TiAlSiN coated drills were tested under accelerated machining conditions by drilling a 12mmthick 304 stainless steel plate. Under dry conditions the uncoated drill bits failed after drilling 50 holes, whereas, TiAlSiN coated drill bits (Si = 5.5 at.%) drilled 714 holes before failure. Results indicated that for TiAlSiN coated drill bits the tool life increased by a factor of more than 14

Performance evaluation of TiAlCrYN nanocomposite coatings deposited using four-cathode reactive unbalanced pulsed direct current magnetron sputtering system

Approximately 1.5e2.5 mm thick nanocomposite coatings of TiAlCrYN were deposited using a fourcathode reactive unbalanced pulsed direct current magnetron sputtering system from the sputtering of Ti, Al, Cr, and Y targets in Ar þ N2 plasma. The TiAlCrYN nanocomposite coatings were deposited on various substrates such as high speed steel (HSS) drill bits, mild steel and silicon. TiAlCrYN coatings with almost similar mechanical properties but with different Ti, Al, Cr and Y contents were prepared to study their thermal stability and machining performance. The structural and mechanical properties of the coatings were characterized using X-ray diffraction and nanoindentation technique, respectively. The elemental composition, bonding structure, surface morphology and cross-sectional data were studied using energy-dispersive X-ray analysis, X-ray photoelectron spectroscopy and field-emission scanning electron microscopy, respectively. Nanoscratch tests were performed to determine the adhesive strength of the coatings. The corrosion behavior of TiAlCrYN nanocomposite coatings on mild steel substrate was studied using potentiodynamic polarization in a 3.5% NaCl solution. Micro-Raman pectroscopy was used to characterize the structural changes as a result of heating of the nanocomposite coatings in air (600e 1000 �C). TiAlCrYN coatings prepared at 17 at.% Ti, 13 at.% Al, 21 at.% Cr and 1 at.% Y exhibited thermal stability as high as 900 �C in air (denoted as Sample 3). For the performance evaluation, the TiAlCrYN coated HSS drill bits were tested under accelerated machining conditions. With a drill speed of 800 rpm and a feed rate of 0.08 mm/rev the TiAlCrYN coated HSS drill bits (Sample 3) averaged 657 holes, while drilling a 12 mm thick 304 stainless steel plate under dry conditions, before failure. Whereas, the uncoated drill bits failed after drilling 50 holes under the same machining conditions. Results indicated that for the HSS drill bits coated with TiAlCrYN, the tool life increased by a factor of more than 12

Magnetic Stress-Driven Metal-Insulator Transition in Strongly Correlated Antiferromagnetic CrN

Traditionally, the Coulomb repulsion or Peierls instability causes the metal-insulator phase transitions instrongly correlated quantum materials. In comparison, magnetic stress is predicted to drive the metalinsulator transition in materials exhibiting strong spin-lattice coupling. However, this mechanism lacksexperimental validation and an in-depth understanding. Here we demonstrate the existence of the magneticstress-driven metal-insulator transition in an archetypal material, chromium nitride. Structural, magnetic,electronic transport characterization, and first-principles modeling analysis show that the phase transitiontemperature in CrN is directly proportional to the strain-controlled anisotropic magnetic stress. Thecompressive strain increases the magnetic stress, leading to the much-coveted room-temperature transition.In contrast, tensile strain and the inclusion of nonmagnetic cations weaken the magnetic stress and reducethe transition temperature. This discovery of a new physical origin of metal-insulator phase transition thatunifies spin, charge, and lattice degrees of freedom in correlated materials marks a new paradigm and couldlead to novel device functionalities