We grew vertically aligned carbon nanotubes ͑CNTs͒ using microwave plasma-enhanced ͑MPE͒ and thermal chemical-vapor deposition ͑CVD͒ and characterized their field emission properties. We observe that the flickering and instability in the field emission are due to the metal particles present on the field-emission array ͑FEA͒ surface, particularly from the MPECVD-grown samples. The existence of metal particles is an obstacle to obtaining reliable emission properties. The emission properties of the CNT-FEA are studied as a function of gas-exposure time with hydrogen, nitrogen, and oxygen gases. Gas exposures affected turn-on voltage, hysteresis, and the slope of Fowler-Nordheim plots. We observe that the saturation of emission currents is attributed to gas adsorbates present on the surface of the FEA. Oxygen exposures induce more severe degradation on the field-emission properties than nitrogen, whereas emission properties are improved by hydrogen gas exposures that clean the surface of emitters. In addition, hydrogenation of carbon nanotubes has technical importance for activation of the CNT-FEA.

Co/Cu͑111͒ multilayers, ͓Co͑17 Å͒/Cu͑8 ÅϽt Cu Ͻ14 Å͔͒ 30 , have been prepared on Co͑70 Å͒ buffer layers on Al 2 O 3 ͑0001͒ substrates by molecular beam epitaxy. From the longitudinal and transverse magnetoresistance ͑MR͒ measurements, it is observed that MRs consist of two components with a small anisotropic MR ͑Ͻ2%͒ component at low field sitting on top of the giant MR ͑up to 22%͒ component at higher field. The AMR effect strongly correlates with the abundance of hcp stacking of Co, which tends to decrease with the increasing of Cu spacer thickness. The AMR saturation fields ͑1-3 kOe͒ coincides with those of the magnetization. It is suggested that the observed AMR effect is due to scattering from the hcp-phase Co layers in the multilayers. This together with the large saturation field ͑30-40 kOe͒ obtained from the entire MR curves indicate that the observed GMR effect may result from the Co-Cu interfacial spin-dependent scattering.