Academic literature on the topic 'Nitrogen Vacancies'

While nitrogen doping has been investigated extensively in silicon, there is only limited information on its interaction with vacancies in germanium, despite most point defect processes in germanium being vacancy controlled. Thus, spin polarized density functional theory calculations are used to examine the association of nitrogen with lattice vacancies in germanium and for comparison in silicon. The results demonstrate significant charge transfer to nitrogen from the nearest neighbor Ge and strong N–Ge bond formation. The presence of vacancies results in a change in nitrogen coordination (from tetrahedral to trigonal planar) though the total charge transfer to N is maintained. A variety of nitrogen vacancy clusters are considered, all of which demonstrated strong binding energies. Substitutional nitrogen remains an effective trap for vacancies even if it has already trapped one vacancy.

The amount and defect type of substitutional nitrogen in synthetic diamond strongly influences crystal strength. There is an optimum amount of nitrogen that yields the highest compressive fracture strength for crystals derived from common growth conditions. It is postulated that the role of nitrogen is to charge-balance vacancies created during growth. If too little nitrogen exists in the diamond, vacancies are not charge-balanced and may serve as crack initiation and/or propagation sites. Excess nitrogen above that required to charge-balance vacancies may weaken the lattice by adding local strain to the crystal. IR microscopy indicates that most of the substitutional nitrogen in synthetic diamond is increased in the vicinity of the intersections of growth sectors on the crystal surface. Most surface IR-visible nitrogen is biased toward the (111)–(100) intersection. The bias in incorporation of substitutional nitrogen at external growth sector intersections (i.e., edges and corners) of an industrial high-grade saw diamond crystal influences the progression of fatigue by microfracture during cutting of hard stone.

DFT calculations were performed to study Ta₃N₅(100), (010) and (001) surfaces with oxygen impurities and nitrogen vacancies. The effects of oxygen impurities and nitrogen vacancies on the surface stability and electronic structures of Ta₃N₅surfaces were put forward.

AbstractIn this study low temperature micro-photoluminescence technology was employed to investigate effects of the irradiation and nitrogen concentration on nitrogen-vacancy (NV) luminescence, with the photochromic and vibronic properties of the NV defects. Results showed that the NV luminescence was weakened due to recombination of self-interstitials created by electron irradiation in diamond and the vacancies within the structure of NV centers. For very pure diamond, the vacancies migrated the long distance to get trapped by N atoms only after sufficient high temperature annealing. As with the increase in nitrogen content, the migration distance of vacancies got smaller. The nitrogen also favored the formation of negatively charged NV centers with the donating electrons. Under the high-energy ultraviolet laser excitation, the photochromic property of the NV− center was also observed, though it was not stable. Besides, the NV centers showed very strong broad sidebands, and the vibrations involved one phonon with energy of ~42 meV and another with ~67 meV energy.

We present an experimental study of the longitudinal and transverse relaxation of ensembles of negatively charged nitrogen-vacancy (NV−) centers in a diamond monocrystal prepared by 1.8 MeV proton implantation. The focused proton beam was used to introduce vacancies at a 20 µµm depth layer. Applied doses were in the range of 1.5×1013 to 1.5×1017 ions/cm2. The samples were subsequently annealed in vacuum which resulted in a migration of vacancies and their association with the nitrogen present in the diamond matrix. The proton implantation technique proved versatile to control production of nitrogen-vacancy color centers in thin films.

Cette étude met en évidence le rôle des lacunes d’azote et des défauts structuraux dans l’ingénierie de revêtements durs à stabilité de phase améliorée et dont les propriétés mécaniques sont compatibles avec des applications à haute température. Le nitrure de titane et d’aluminium (Ti,Al)N sous forme de revêtements est un matériau de choix pour la protection des outils de coupe pour métaux en raison de sa résistance supérieure à l’oxydation et à l’usure à haute température. La décomposition spinodale à haute température de la phase métastable cubique (Ti,Al)N en domaines cohérents de taille nanométrique de c-TiN et de c-AlN donne une dureté importante aux températures élevées. Un apport thermique encore plus élevé conduit à la transformation de c-AlN en w-AlN, ce qui nuit aux propriétés mécaniques du revêtement. Un moyen de retarder cette transformation est d'introduire des lacunes d'azote. Dans cette thèse, je montre que la combinaison d’une réduction de la teneur globale en azote du revêtement c-(Ti,Al)Ny(y <1) avec une faible tension de polarisation du substrat lors du dépôt par arc cathodique induit un retard encore plus prononcé de la transformation de la phase c-AlN en w-AlN. Dans de telles conditions, le durcissement par vieillissement est conservé jusqu'à 1100 ° C, ce qui correspond à la température la plus élevée signalée pour les films de (Ti,Al)N. Au cours des opérations de coupe, le mécanisme d'usure des films c-(Ti0.52Al0.48)Ny déposés par arc cathodique avec des teneurs en N de y = 0.92, 0.87 et 0.75 est influencé par l'interaction des lacunes d'azote, de la microstructure et des réactions chimiques avec le matériau de la pièce. Le revêtement y = 0.75 contient le plus grand nombre de macroparticules et présente, après usinage, une microstructure non homogène qui en abaisse la résistance à l'usure sur les flancs et les cratères. Le durcissement par vieillissement de l'échantillon y = 0.92 entraîne une résistance supérieure à l'usure sur le flanc, tandis que la structure dense de l'échantillon y = 0.87 empêche l'usure chimique qui se traduit par une excellente résistance à l'usure sur les cratères. Des films hétéroépitaxiés c-(Ti1-x, Alx)Ny (y = 0.92, 0.79 et 0.67) ont été déposés sur des substrats de MgO(001) et (111) en utilisant une technique de pulvérisation magnétron pour examiner en détail les défauts structuraux pendant la décomposition spinodale. À 900 °C, les films se décomposent pour former des domaines cohérents riches en c-AlN et c-TiN de forme allongée le long de la direction <001>. Les cartographies de déformation montrent que la plupart des contraintes se trouvent près de l'interface des domaines ségrégés et à l'intérieur des domaines c-TiN. Les dislocations s'agrègent favorablement dans c-TiN plutôt que dans c-AlN car ce dernier a une directionnalité plus forte des liaisons chimiques covalentes. À température élevée, la taille de domaine des films de c- (Ti, Al)Ny orientés (001) et (111) augmente avec la teneur en azote. Cela indique qu'il y a un retard dans le grossissement dû à la présence de plus de lacunes d’azote dans le film. [...]
This study highlights the role of nitrogen vacancies and defect structures in engineering hard coatings with enhanced phase stability and mechanical properties for high temperature applications. Titanium aluminum nitride (Ti,Al)N based materials in the form of thin coatings has remained as an outstanding choice for protection of metal cutting tools due to its superior oxidation resistance and high-temperature wear resistance. High-temperature spinodal decomposition of metastable (Ti,Al)N into coherent c-TiN and c-AlN nm-sized domains results in high hardness at elevated temperatures. Even higher thermal input leads to transformation of c-AlN to w-AlN, which is detrimental to the mechanical properties of the coating. One mean to delay this transformation is to introduce nitrogen vacancies. In this thesis, I show that by combining a reduction of the overall N-content of the c-(Ti,Al)Ny (y < 1) coating with a low substrate bias voltage during cathodic arc deposition an even more pronounced delay of the c-AlN to w-AlN phase transformation is achieved. Under such condition, age hardening is retained until 1100 °C, which is the highest temperature reported for (Ti,Al)N films. During cutting operations, the wear mechanism of the cathodic-arc-deposited c-(Ti0.52Al0.48)Ny with N-contents of y = 0.92, 0.87, and 0.75 films are influenced by the interplay of nitrogen vacancies, microstructure, and chemical reactions with the workpiece material. The y = 0.75 coating contains the highest number of macroparticles and has an inhomogeneous microstructure after machining, which lower its flank and crater wear resistance. Age hardening of the y = 0.92 sample causes its superior flank wear resistance while the dense structure of the y = 0.87 sample prevents chemical wear that results in excellent crater wear resistance. Heteroepitaxial c-(Ti1-x,Alx)Ny (y = 0.92, 0.79, and0.67) films were grown on MgO(001) and (111) substrates using magnetron putter deposition to examine the details of their defect structures during spinodal decomposition. At 900 °C, the films decompose to form coherent c-AlN- and c-TiN- rich domains with elongated shape along the elastically soft <001> direction. Deformation maps show that most strains occur near the interface of the segregated domains and inside the c-TiN domains. Dislocations favorably aggregate in c-TiN rather than c-AlN because the later has stronger directionality of covalent chemical bonds. At elevated temperature, the domain size of (001) and (111)- oriented c-(Ti,Al)Ny films increases with the nitrogen content. This indicates that there is a delay in coarsening due to the presence of more N vacancies in the film. The structural and functional properties (Ti1-x,Alx)Ny are also influenced by its Al content (x). TiN and (Ti1-x,Alx)Ny (y = 1, x = 0.63 and x = 0.77) thin films were grown on MgO(111) substrates using magnetron sputtering technique. Both TiN and Ti0.27Al0.63N films are single crystals with cubic structure. (Ti0.23,Al0.77)N film has epitaxial cubic structure only in the first few atomic layers then it transitions to an epitaxial wurtzite layer, with an orientation relationship of c-(Ti0.23,Al0.77)N(111)[1-10]ǀǀw-(Ti0.23,Al0.77)N(0001)[11-20]. The w-(Ti0.23,Al0.77)N shows phase separation of coherent nm-sized domains with varying chemical composition during growth. After annealing at high temperature, the domains in w-(Ti0.23,Al0.77)N have coarsened. The domains in w-(Ti0.23,Al0.77)N are smaller compared to the domains in c-(Ti0.27,Al0.63)N film that has undergone spinodal decomposition. The results that emerged from this thesis are of great importance in the cutting tool industry and also in the microelectronics industry, because the layers examined have properties that are well suited for diffusion barriers

Chromium doped aluminum nitride (AlN: Cr) thin films were grown on silicon, glass and copper substrates by DC and RF magnetron sputtering co-deposition. After growth, thin films on silicon substrates were annealed at 1373 K for 30 min in N2 atmosphere. The AlN: Cr thin films were characterized by x-ray diffraction for structural analysis, by FS5 spectrofluorometer for the study of photoluminescence, absorption, transmission, and chromaticity. As-deposited and annealed silicon substrate and as-deposited glass substrate thin films of AlN: Cr exhibited intense photoluminescence emission in the range of 400 to 679.5 nm. Spectral evidence demonstrated conclusively that the AlN: Cr thin films on as-deposited glass substrate and annealed silicon substrate have excellent photoluminescence emission which is due to both AlN (host) and Cr3+ ions. The reasons of photoluminescence of AlN in the visible region are surface defects and impurities. Impurities become the cause to produce different types of defects and vacancies just like oxygen point defects (O+N), nitrogen vacancies (VN) and various defect complexes (V3-Al – 3 O+N). It may also be due to the recombination of photogenerated hole with the electron occupied by the nitrogen vacancies and due to the transition between deep level of (V3-Al – 3 O+N) defect complexes and shallow level of VN and the reason behind the photoluminescence of Cr3+ ions is due to vibrational energy levels 4T1 and 4T2 and due to 4T1→4A2 and 4T2→4A2 transitions. AlN: Cr thin films can give better results in the applications like light emitting diodes (LEDs), laser diodes (LDs), field emission displays, microelectromechanical system (MEMS), optical MEMS and biomedical applications. Key words: III-V Semiconductor Material, Thin films, Photoluminescence Mechanism

Well dispersed Aluminum Nitride (AlN) nanopowder and AlN thin film were compared to observe their structural and luminescence properties. AlN thin films were deposited on silicon and copper substrates by RF magnetron sputtering. PL peaks analysis indicated the same pattern of emission peaks over different excitation wavelengths ranging from 200 nm to 300 nm for both the AlN nanopowder and thin film, nearly 100 -1000 times PL increment observed in AlN nanopowder. It is suggested that the reason for PL of AlN material is due to surface defects and impurities like oxygen-related point defects (O+N), nitrogen vacancies (VN), the transition from the donor level of VN (nitrogen-vacancy) to the acceptor level of AlN (antisites defects), and various defect complexes (V3-Al – 3 O+N) are responsible for the enhanced observed emission peaks. With well-defined emission curves, AlN Nanopowder and thin films are observed to be good substrate and insulator material for microelectronic circuits, Light Emitting Diodes, Laser Diodes, and in biomedical applications such as bioimaging and biosensors.