TECHNOLOGY FOCUS - ELECTRICAL POWER AND ENERGY - Preferred Process: The step (a) is performed by electroless deposition. The step (b) is performed at a potential whose value is equal to or less than two-thirds or one-third the potential at which bulk deposition of the second solid occurs. The tubular passage is: open at both ends; and closed at one end. The tubular passage has a central axis, the method further comprises separating (A) from the form after (b), and the radial growth of (b) is inward toward the axis. (A) has an outer surface and inner surface, the method further comprises separating (A) from the form before (b), and the radial growth is both inward from the inner surface and outward from the outer surface.Preferred Components: The first and second solids are: electrical conductors; and semiconductors. The first and second solids are: a semiconductor and the other is an electrical conductor; a semiconductor and the other is an electrical insulator; and an electrical insulator and the other is an electrical conductor. The well diameter is 5- 200 (preferably 10-50) nm.Preferred Method: The method further comprises: depositing at least one additional layer of solid over the layer of the second solid; and doping one of the first and second solids with a n-type or p-type dopant. The form is a track-etched polymer nanoporous membrane (track-etched polycarbonate).    TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Material: The first (silver, gold (both preferred), copper, nickel, palladium and platinum) and second solids (tellurium, cadmium, zinc, sulfur (all preferred), selenium, polonium, phosphorus, arsenic, antimony, bismuth, carbon, silicon, germanium, tin, lead, aluminum, gallium, indium, thallium, , mercury, and compounds and alloys of these elements) are metals and the first solid is a metal that is substantially less reactive with other elements than the second solid. The tubular passages have diameters within the range 5-200 (preferably 30-150) nm. The nanotube has a tube wall thickness 10-100 (preferably 30-150) nm. EXAMPLE - Nanotubes were formed within the pores of the polycarbonate track-etched membranes (with hydraulic pore diameters of approximately 104 nm, a pore density of approximately 6 pores per square micron, and a membrane thickness of 6 microns) by electroless deposition of metallic gold on the inner surfaces of the pores, which process comprises first sensitizing the pore surfaces with tin ion (Sn+2), treating the sensitized surfaces with silver ion (Ag+2), and finally depositing metallic gold from an aqueous solution of Na3Au(SO3)2 (0.0079 M), sodium sulfite (0.127 M), and formaldehyde (0.625 M). Deposition was performed at pH of 10 and 0.5degreesC for 4 hours, resulting in a reduction in the hydraulic pore size to 35 nm. The resulting nanotubes thus had a wall thickness of approximately 35 nm. The nanotube-containing membranes were then immersed in 25% nitric acid for 12 hours. In addition to removing all residual tin and silver, this left a small annular gap between the nanotubes and the pore walls. An electrochemical cell for depositing tellurium on the inner surfaces of the gold nanotubes was then configured with the gold nanotubes as the working electrode, platinum wire as the counter electrode, and silver/silver chloride 3M as a reference electrode. The nanotube-containing membrane and electrodes were immersed in an electrolyte solution containing tellurium oxide (0.1 mM), cadmium sulfate (IMM), and sulfuric acid (50 mM), and a potential of -62 mV was applied over 8 hours. The membrane was then dissolved in dichloromethane to release the nanocables. To enhance visualization of the different layers of the nanocables, the gold was partially removed from the nanocables by etching with potassium iodide.