We have developed a new method of capacitance profiling which is greatly superior to standard profiling techniques for materials like amorphous silicon that contain high densities of deep gap states. This technique, which makes use of the variation of the junction capacitance with the alternating voltage amplitude, is largely immune to the effects of surface states and is readily interpreted in terms of a simple integral over the density of states, g(E). This method is applicable to both doped and semi-insulating undoped samples.

A hollow cathode discharge (HCD) is described that produces a highly ionized steady-state plasma (ne≈1013−1014/cm3) at a temperature 1–10 eV, in a volume as large as 104 cm3, with background neutral gas density ≈1013/cm3. The HCD is generated by the prescription: gas flow (H2, He, A, or N2) 0.05–2 cc STP/sec through a refractory metal hollow cathode tube into a vacuum; any anode; 20–200 V dc applied. An axial induction 100–1000 G is used to collimate the discharge and to aid in starting by rf excitation. The HCD runs from the cathode interior, deep enough that p0d≈1 cm×mm Hg. Current range is 2.0–300 A. Various electrode configurations and a wide range of operating parameters have been studied. The external plasma density and temperature were measured by Langmuir probes. A discussion is given of the confinement mechanism and of the energy balance, both in the external plasma and in the region of the cathode itself.

Rapid voltage reduction across porous anodic coatings results in zero current, and a relatively long time is required for recovery to the new equilibrium current. The recovery time is dependent on the voltage change, rate of change, and electrolyte temperature. Capacity measurements show that physical thinning occurs only when current begins to increase late in the recovery period. This behavior appears inconsistent with the conventional pore base dissolution mechanism of porous oxide growth. ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 157.182.150.22 Downloaded on 2015-06-29 to IP

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