NOVELTY - Composition of matter comprises nanowires on a substrate, where the nanowires have been grown epitaxially on the substrate in the presence of a metal catalyst such that a catalyst deposit is located at the top of at least some of the nanowires, where the nanowires comprise at least one group III-V compound or at least one group II-VI compound or comprises at least one non carbon group IV element; and where a graphitic layer is in contact with at least some of the catalyst deposits on top of the nanowires.    USE - The composition of matter is useful for preparing device, e.g. optical or electronic device, e.g. solar cell (claimed). It can also be used in sensors, nanowire light-emitting diodes (LEDs) and nanowire solar cells.    ADVANTAGE - By using the composition of matter, the superior properties of the graphitic layers as top contact material can be fully utilized in resulting opto-electronic devices. Unlike other semiconductor substrates, graphitic substrates are thin, light, and flexible, yet very strong, and can be easily transferred onto any other substrates. The metal catalytic particles that remain on top of the nanowires after the nanowire growth are beneficially used as an intermediate material to enhance the electrical contact of nanowires to the top-contacted graphitic layers.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for:    (1) a process for preparing composition of matter involving: (a) providing group II-VI elements or group III-V elements or at least one non carbon group IV element to the surface of a substrate, preferably via a molecular beam; (b) epitaxially growing nanowires from the surface of the substrate in the presence of a metal catalyst such that a catalyst deposit remains on the top of at least some of the nanowires; and (c) contacting the metal catalyst deposits with a graphitic layer such that a graphitic layer is in contact with at least some of the catalyst deposits on top of the nanowires; and    (2) a device comprising the composition, e.g. an optical or electronic device, e.g. a solar cell.