Raman and various photoluminescence (PL) techniques were employed to investigate the role of nitrogen doping on the optical spectra of chemical-vapor-deposited (CVD) diamond films and to determine the origin of the characteristic broadband luminescence which is observed from approximately 1.5 to 2.5 eV and centered at ∼2 eV. The PL transitions attributed to the zero-phonon lines (ZPL) of nitrogen centers are observed at 1.945 and 2.154 eV. A new possible nitrogen center at 1.967 eV is also observed as well as the band A luminescence centered at ∼2.46 eV. The experimental results preclude the possibility of the broadband PL being due to electron-lattice interaction of the nitrogen ZPL centers. We establish the presence of an in-gap state distribution in CVD diamond films attributed to the sp2 disordered phase and show that its optical transitions are the likely cause of the broadband luminescence. A model of the in-gap state distribution is presented which is similar to models previously developed for amorphous materials.

The photoluminescence ͑PL͒ in as-received and milled Si and SiO 2 powder is reported. The Si and SiO 2 powder is characterized by chemical analysis, Raman scattering, x-ray photoelectron spectra, infrared absorption, x-ray diffraction, and differential thermal analysis. The results indicate that the Si powder has amorphous Si oxide and suboxide surface layers. The milling of Si powder results in the formation of nanocrystalline/ amorphous Si components. An amorphous SiO 2 component is formed by milling crystalline SiO 2 . The PL spectra for as-received Si, milled Si, and SiO 2 powder exhibit similar peak shapes, peak maxima, and full width at half maximum values. For both the as-received and the milled Si powder, experimental results appear to exclude mechanisms for PL related to an amorphous Si component or Si-H or Si-OH bonds, or the quantum confinement effect. Similarly, for milled SiO 2 powder mechanisms for PL do not appear related to Si-H or Si-OH bonds. Instead the greatly increased intensity of PL for milled SiO 2 can be related to both the increased volume fraction of the amorphous SiO 2 component and the increased density of defects introduced in the amorphous SiO 2 upon milling. It is suggested that the PL for as-received Si, milling-induced nanocrystalline/ amorphous Si, and milled SiO 2 results from defects, such as the nonbridging oxygen hole center, in the amorphous Si suboxide and/or SiO 2 components existing in these powder samples. The PL measurement for milled SiO 2 is dependent on air pressure whereas that for as-received SiO 2 is not, suggesting that new emitting centers are formed by milling.

The effect of Ta and Ta/Cu seed layers, and Ta and Cu cap layers on the effective magnetic thickness of ultrathin permalloy (Ni81Fe19) was investigated for MRAM applications. The films were deposited by Ion Beam Deposition. The magnetic moment of each as-deposited permalloy film was measured using a B-H looper and a SQUID magnetometer. The films were further annealed at either 525 K for 1/2 h or 600 K for 1 h to study the effect of thermally driven interdiffusion on the magnetic moment of the permalloy film. Our theoretical calculations showed that the presence of 12% intermixing at the interface reduces the Ni moments to zero. Experimentally, it was shown that the tantalum rather than the copper interfaces are primarily responsible for the magnetically dead layers. The Ta seed layer interface produces a loss of moment equivalent to a magnetically dead layer of thickness 0.6±0.2 nm. The Ta metal in the cap layer results in a loss of moment equivalent to a dead layer of thickness 1.0±0.2 nm. Upon annealing, thermally driven interdiffusion is concluded to have a strong effect on the Ta(seed)/ Ni81Fe19 as-deposited interface, based on the doubling of the magnetically dead layer to 1.2±0.2 nm. The Ni81Fe19/Ta(cap) as-deposited interface slightly increases its equivalent magnetically dead layer upon annealing to 1.2±0.2 nm. As-deposited interfaces of Ta(seed)/permalloy and permalloy/Ta(cap) are not chemically equivalent and result in different magnetically dead layers, whereas after annealing to 600 K both interfaces attain comparable intermixing and magnetically dead layers. It was also shown that a half-hour anneal at the lower 525 K annealing temperature, which is closer to the actual processing temperature, results in only slight increase of the magnetically dead layer at both interfaces.

Polycrystalline diamond thin films have been formed on single crystal silicon field emitters using bias-enhanced nucleation in a microwave plasma chemical vapor deposition system. A diamond nucleation density greater than 1010/cm2 with small grain sizes (<25 nm) was achieved on the surfaces of silicon emitters with nanometer scale curvature. Field emission from these diamond coated silicon emitters exhibited significant enhancement compared to the pure Si emitters both in total emission current and stability. Using a Fowler–Nordheim analysis a very large effective emitting area of nearly 10−11 cm2 was obtained from the diamond coated Si emitters compared to that of uncoated Si emitters (10−16 cm2). This area was found to be comparable to the entire tip surface area.

Emission stability of a diamond-like carbon coated metal-tip field emitter array