The large-scale assembly of nanowires with controlled orientation on surfaces remains one challenge preventing their integration into practical devices. We report the vapor-liquid-solid growth of aligned, millimeter-long, horizontal GaN nanowires with controlled crystallographic orientations on different planes of sapphire. The growth directions, crystallographic orientation, and faceting of the nanowires vary with each surface orientation, as determined by their epitaxial relationship with the substrate, as well as by a graphoepitaxial effect that guides their growth along surface steps and grooves. Despite their interaction with the surface, these horizontally grown nanowires display few structural defects, exhibiting optical and electronic properties comparable to those of vertically grown nanowires. This paves the way to highly controlled nanowire structures with potential applications not available by other means.

The large-scale integration of nanowires into practical devices is hindered by the limited ability to controllably assemble these nanoscale objects on surfaces. Following our first report on the guided growth of millimeter-long horizontal nanowires with controlled orientations, here we demonstrate the generality of the guided growth approach by extending it from GaN nanowires to ZnO nanowires. We describe the guided growth of horizontally aligned ZnO nanowires with controlled crystallographic orientations on eight different planes of sapphire, including both flat and faceted surfaces. The growth directions, crystallographic orientation, and faceting of the nanowires are constant for each surface plane and are determined by their epitaxial relation with the substrate, as well as by a graphoepitaxial effect that guides their growth along surface steps and grooves. These horizontal ZnO nanowires exhibit optical and electronic properties comparable to those of vertically grown nanowires, indicating a low concentration of defects. While the guided growth of ZnO nanowires described here resembles the guided growth of GaN nanowires in its general aspects, it also displays notable differences and qualitatively new phenomena, such as the controlled growth of nanowires with vicinal orientations, longitudinal grain boundaries, and thickness-dependent orientations. This article proves the generality of the guided growth phenomenon, which enables us to create highly controlled nanowire structures and arrays with potential applications not available by other means.

The ability to assemble discrete nanowires (NWs) with nanoscale precision on a substrate is the key to their integration into circuits and other functional systems. We demonstrate a bottom-up approach for massively parallel deterministic assembly of discrete NWs based on surface-guided horizontal growth from nanopatterned catalyst. The guided growth and the catalyst nanopattern define the direction and length, and the position of each NW, respectively, both with unprecedented precision and yield, without the need for postgrowth assembly. We used these highly ordered NW arrays for the parallel production of hundreds of independently addressable single-NW field-effect transistors, showing up to 85% yield of working devices. Furthermore, we applied this approach for the integration of 14 discrete NWs into an electronic circuit operating as a three-bit address decoder. These results demonstrate the feasibility of massively parallel "self-integration" of NWs into electronic circuits and functional systems based on guided growth.T he sustained progress in semiconductor technology introduces new challenges associated with the scaling and functionality of nanosize components. In the face of these challenges, alternative unconventional device and fabrication concepts based on bottom-up assembly of synthetic nanostructures are being intensively explored (1). These nanostructures, such as quantum dots (2), nanotubes (3), and nanowires (NWs) (4), can be chemically synthesized with exquisite control over their structures and properties down to the atomic level. On the other hand, their self-assembly alone is unlikely to produce the arbitrary geometries and long-range order that are required for their integration into functional systems. To realize such systems, bottomup assembly may be used as a complementary step in a sequence of top-down fabrication processes. Such a hybrid top-down/ bottom-up approach can be based on the directed self-assembly of building blocks onto a lithographically produced template to fit the design of an integrated functional system. Thus, the building blocks integrate themselves into the system, as one of the layers in the overall design. Here we demonstrate the feasibility of this "self-integration" concept with the parallel fabrication of large numbers of devices and complex circuits, based on guided growth of horizontal NWs (5).NWs are attractive building blocks for the bottom-up assembly of nanoscale devices and functional systems with potential applications in nanoelectronics (6), photonics (7), renewable energy (8), and biology (9). They can be synthesized with precisely controlled nanoscale dimensions and chemical compositions (10). Moreover, they may be structured to possess unique electronic properties, such as ballistic conductivity due to confinement of a 1D charge-carrier gas in core-shell NWs (11). The potential of NW-based electronics has been demonstrated for various NW materials (12). However, most studies were done at the single-device level. The main obstacle toward NW integration...

We report the guided growth of highly coherent, horizontal GaN nanowires (NWs) on atomically flat singular SiC (0001) and on periodically stepped vicinal SiC (0001) substrates. On singular SiC (0001) the NWs grow in six symmetry-equivalent directions, while on vicinal SiC (0001) the NWs grow only in the two directions parallel to the atomic step edges. All of the NWs have the same epitaxial relations with the substrate on both singular and vicinal (0001). Owing to the low mismatch (~3.4%) with the substrate, the NWs grow highly coherent, with a much lower density of misfit dislocations than previously observed on sapphire. This is also the first observation of NW VLS growth along atomic steps. Epitaxially coherent guided NWs have potential uses in many fields, including high-power electronics, light-emitting diodes (LEDs), and laser diodes.

The guided growth of horizontal nanowires has so far been demonstrated on a limited number of substrates. In most cases, the nanowires are covalently bonded to the substrate where they grow and cannot be transferred to other substrates. Here we demonstrate the guided growth of well-aligned horizontal GaN nanowires on quartz and their subsequent transfer to silicon wafers by selective etching of the quartz while maintaining their alignment. The guided growth was observed on different planes of quartz with varying degrees of alignment. We characterized the crystallographic orientations of the nanowires and proposed a new mechanism of "dynamic graphoepitaxy" for their guided growth on quartz. The transfer of the guided nanowires enabled the fabrication of back-gated field-effect transistors from aligned nanowire arrays on oxidized silicon wafers and the production of crossbar arrays. The guided growth of transferrable nanowires opens up the possibility of massively parallel integration of nanowires into functional systems on virtually any desired substrate.