NOVELTY - A nano-twinned nanostructure array comprises several nanostructures, where each nanostructure comprises uniformly aligned nano-twins either perpendicular or inclined by about 1-90 degrees from the perpendicular of pillar-axis with no grain-boundaries.    USE - As a nano-twinned nanostructure array; for making nano-twined nanopillar composition; as nano-twinned copper nanopillar array; and in electrical, optical and micro-electro-mechanical system (MEMS) device (claimed). The nanostructures are also used in numerous electrical, optical, biological, mechanical and other technological devices such as e.g. solar cells, photo-detectors, photonic crystals, memory devices, nano-filtration, fuel cells, and artificial kidneys.    ADVANTAGE - The nanopillars have reduced stress-induced voiding. The array effectively satisfies the small dimension requirements of many electrical and optical devices. The array provides free-standing individual nano-twinned Cu nanopillar with no grain boundaries. The nano-twinned nanostructure has increased strength and lacks defects found in conventional nano-structures. The array exhibits improved conductivity (i.e. reduced resistance) compared to non-twinned structures and shows improved mechanical strength.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for the following:    (1) process for preparing the nano-structure involving coating a substrate (10) with a conductive layer (20); coating the conductive layer with a resist polymer (30); using a lithography technique to pattern (35) a template (40) into the resist polymer; electrodepositing a metal into the template, where the template comprises template-cathode and where the process further includes a non-patterned cathode, where the total surface area of template-cathode and non-patterned cathode is equal to the surface area of anode; and optionally removing the resist; and    (2) a method of making nano-twinned nanopillar composition involving the preparation process.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic view of nano-twinned nanostructure array fabrication.    Semi-rigid substrate (10)    Conductive layer (20)    Resist polymer (30)    Pattern (35)    Template (40)    Fill material (45)