The field-emission properties of cold cathodes produced using nano-porous anodic aluminum oxide (AAO) templates are reported. Several types of field emitters were fabricated: aligned copper nanowires grown halfway up the parallel nano-pores of the AAO; aligned multiwalled carbon nanotubes grown to the top of the pores; surfaces overgrown with random tangles of carbon nanotubes; and empty AAO templates. Significant field-emission currents (field enhancement values ∼ 1800) were obtained at threshold voltages as low as 80 V (corresponding to fields of 3–4 V/μm) on samples of nanotube tangles. Perfectly aligned carbon nanotubes were less efficient field emitters and had lower field enhancement values. These observations are explained in terms of the mean separation of active tips in the two sets of samples. Empty templates and metal nanowire arrays show lower field enhancements and higher threshold electric fields (40–70 V/μm). In these samples significant field-emission currents are produced at relatively low applied voltages of 110–300 V due to the small inter-electrode separations achieved on depositing a metal grid directly on the surface of the porous template.

Tunneling spectroscopy studies on oxidized and bare surfaces of icosahedral i-AlPdRe, i-AlCuFe, and approximant a-AlMnSi phases reveal specific features of the density of states (DOS) close to the Fermi level as compared to the crystalline nonapproximant v-AlCuFe phase. The Fermi energy lies in the middle of a narrow pseudogap of about 50 meV width. For higher energies, the DOS exhibits a square root energy dependence attributed to electron-electron interaction effects. The DOS differs from the linear muffin tin orbital calculated DOS and the possible roles of electron scattering and inhomogeneous electronic structure close to the surface are discussed.[S0031-9007(96)

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The fabrication and electrical properties of high-density arrays of cylindrical nanoscale capacitors grown in anodic aluminum oxide templates is described. Using chemical vapor deposition, alternating metallic (carbon) and insulating (boron nitride) layers are created within the template pores, thereby forming composite metal/insulator/metal nanotubules. With the metal electrodes evaporated on the two sides of the template, the structure is converted to an array of nanocapacitors connected in parallel. For 50-μm-thick templates, specific capacitances as high as 2.5 μF/cm2 were measured and capacitances as high as 13 μF/cm2 should be attainable by optimizing the insulating layer properties. The fabrication process can be made compatible with the silicon technology and might, therefore, be used to fabricate high-capacitance elements on tightly packed chips. At the same time, the leakage resistance of the arrays fabricated in the preliminary studies reported here is rather low, presumably due to the contamination of the insulating layer.

Coulomb blockade ͑CB͒ was observed in Al/aluminum oxide/Ni nanowire single-junction arrays fabricated by electrochemical deposition of Ni into porous aluminum oxide nanotemplates. The bias dependence of the tunneling current and the temperature dependence of the zero-bias anomalies observed in the tunneling spectra are shown to accord well with the theory of Nazarov for CB in systems where the leads play a significant role. Direct scanning tunneling microscopy measurements of the nanowire leads resistance confirms it to be the regime required by the theory. ͓S0163-1829͑98͒02521-1͔

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The resistance and tunneling spectra of samples formed by depositing silver electrodes at the two ends of aligned, template-grown, carbon nanotube arrays were measured in the temperature range 0.67–440 K. Two types of samples were fabricated, one with small oxide tunnel junctions separating the carbon nanotubes from the metal electrodes, the other with a significant Al2O3 tunnel barrier. The measurements indicate the presence of three regimes for dI/dV(V). For T>220 K, dI/dV(V) and the zero-bias conductivity show a broad minimum and an activation temperature dependence suggesting semiconductor behavior. In the temperature range 10<T<140 K, the zero-bias conductivity shows a square-root temperature dependence. For T<2 K, a very steep rise in the zero-bias tunneling resistance is observed with a strong simultaneous suppression of the tunneling conductivity near the Fermi energy. Coulomb blockade is suggested as a plausible explanation of the observed behavior.

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